unfinished partial work

10 files changed, 3061 insertions, 19 deletions

diff --git a/tests/helpers.py b/tests/helpers.py
new file mode 100644
index 0000000..df474b0
--- /dev/null
+++ b/tests/helpers.py
@@ -0,0 +1,51 @@
+# SPDX-License-Identifier: CC0-1.0
+
+# Copyright (C) 2022 Wojtek Kosior <koszko@koszko.org>
+#
+# Available under the terms of Creative Commons Zero v1.0 Universal.
+
+import re
+
+variable_word_re = re.compile(r'^<(.+)>$')
+
+def process_command(command, expected_command):
+    """Validate the command line and extract its variable parts (if any)."""
+    assert len(command) == len(expected_command)
+
+    extracted = {}
+    for word, expected_word in zip(command, expected_command):
+        match = variable_word_re.match(expected_word)
+        if match:
+            extracted[match.group(1)] = word
+        else:
+            assert word == expected_word
+
+    return extracted
+
+def run_missing_executable(command, **kwargs):
+    """
+    Instead of running a command, raise FileNotFoundError as if its executable
+    was missing.
+    """
+    raise FileNotFoundError('dummy')
+
+class MockedCompletedProcess:
+    """
+    Object with some fields similar to those of subprocess.CompletedProcess.
+    """
+    def __init__(self, args, returncode=0,
+                 stdout='some output', stderr='some error output',
+                 text_output=True):
+        """
+        Initialize MockedCompletedProcess. Convert strings to bytes if needed.
+        """
+        self.args       = args
+        self.returncode = returncode
+
+        if type(stdout) is str and not text_output:
+            stdout = stdout.encode()
+        if type(stderr) is str and not text_output:
+            stderr = stderr.encode()
+
+        self.stdout = stdout
+        self.stderr = stderr
diff --git a/tests/test_build.py b/tests/test_build.py
new file mode 100644
index 0000000..868594e
--- /dev/null
+++ b/tests/test_build.py
@@ -0,0 +1,818 @@
+# SPDX-License-Identifier: CC0-1.0
+
+# Copyright (C) 2022 Wojtek Kosior <koszko@koszko.org>
+#
+# Available under the terms of Creative Commons Zero v1.0 Universal.
+
+# Enable using with Python 3.7.
+from __future__ import annotations
+
+import pytest
+import json
+import shutil
+import functools as ft
+
+from tempfile import TemporaryDirectory
+from pathlib import Path, PurePosixPath
+from hashlib import sha256
+from zipfile import ZipFile
+from contextlib import contextmanager
+
+from jsonschema import ValidationError
+
+from hydrilla import _version, json_instances, versions
+from hydrilla.json_instances import _schema_name_re
+from hydrilla.builder import build, local_apt
+from hydrilla.builder.common_errors import *
+
+from .helpers import *
+
+here = Path(__file__).resolve().parent
+
+expected_generated_by = {
+    'name': 'hydrilla.builder',
+    'version': _version.version
+}
+
+orig_srcdir = here / 'source-package-example'
+
+index_obj = json_instances.read_instance(orig_srcdir / 'index.json')
+
+def read_files(*file_list):
+    """
+    Take names of files under srcdir and return a dict that maps them to their
+    contents (as bytes).
+    """
+    return dict((name, (orig_srcdir / name).read_bytes()) for name in file_list)
+
+dist_files = {
+    **read_files('LICENSES/CC0-1.0.txt', 'bye.js', 'hello.js', 'message.js'),
+    'report.spdx': b'dummy spdx output'
+}
+src_files = {
+    **dist_files,
+    **read_files('README.txt', 'README.txt.license', '.reuse/dep5',
+                 'index.json')
+}
+extra_archive_files = {
+}
+
+sha256_hashes = dict((name, sha256(contents).digest().hex())
+                     for name, contents in src_files.items())
+
+del src_files['report.spdx']
+
+expected_source_copyright = [{
+    'file': 'report.spdx',
+    'sha256': sha256_hashes['report.spdx']
+}, {
+    'file': 'LICENSES/CC0-1.0.txt',
+    'sha256': sha256_hashes['LICENSES/CC0-1.0.txt']
+}]
+
+expected_resources = [{
+    '$schema': 'https://hydrilla.koszko.org/schemas/api_resource_description-1.schema.json',
+    'source_name': 'hello',
+    'source_copyright': expected_source_copyright,
+    'type': 'resource',
+    'identifier': 'helloapple',
+    'long_name': 'Hello Apple',
+    'uuid': 'a6754dcb-58d8-4b7a-a245-24fd7ad4cd68',
+    'version': [2021, 11, 10],
+    'revision': 1,
+    'description': 'greets an apple',
+    'dependencies': [{'identifier': 'hello-message'}],
+    'scripts': [{
+        'file': 'hello.js',
+        'sha256': sha256_hashes['hello.js']
+    }, {
+        'file': 'bye.js',
+        'sha256': sha256_hashes['bye.js']
+    }],
+    'generated_by': expected_generated_by
+}, {
+    '$schema': 'https://hydrilla.koszko.org/schemas/api_resource_description-1.schema.json',
+    'source_name': 'hello',
+    'source_copyright': expected_source_copyright,
+    'type': 'resource',
+    'identifier': 'hello-message',
+    'long_name': 'Hello Message',
+    'uuid': '1ec36229-298c-4b35-8105-c4f2e1b9811e',
+    'version': [2021, 11, 10],
+    'revision': 2,
+    'description': 'define messages for saying hello and bye',
+    'dependencies': [],
+    'scripts': [{
+        'file': 'message.js',
+        'sha256': sha256_hashes['message.js']
+    }],
+    'generated_by': expected_generated_by
+}]
+
+expected_mapping = {
+    '$schema': 'https://hydrilla.koszko.org/schemas/api_mapping_description-1.schema.json',
+    'source_name': 'hello',
+    'source_copyright': expected_source_copyright,
+    'type': 'mapping',
+    'identifier': 'helloapple',
+    'long_name': 'Hello Apple',
+    'uuid': '54d23bba-472e-42f5-9194-eaa24c0e3ee7',
+    'version': [2021, 11, 10],
+    'description': 'causes apple to get greeted on Hydrillabugs issue tracker',
+    'payloads': {
+	'https://hydrillabugs.koszko.org/***': {
+	    'identifier': 'helloapple'
+	},
+	'https://hachettebugs.koszko.org/***': {
+	    'identifier': 'helloapple'
+        }
+    },
+    'generated_by': expected_generated_by
+}
+
+expected_source_description = {
+    '$schema': 'https://hydrilla.koszko.org/schemas/api_source_description-1.schema.json',
+    'source_name': 'hello',
+    'source_copyright': expected_source_copyright,
+    'source_archives': {
+        'zip': {
+            'sha256': '!!!!value to fill during test!!!!',
+        }
+    },
+    'upstream_url': 'https://git.koszko.org/hydrilla-source-package-example',
+    'definitions': [{
+        'type': 'mapping',
+        'identifier': 'helloapple',
+	'long_name': 'Hello Apple',
+        'version': [2021, 11, 10],
+    }, {
+        'type': 'resource',
+        'identifier': 'helloapple',
+        'long_name': 'Hello Apple',
+        'version': [2021, 11, 10],
+    }, {
+        'type':       'resource',
+        'identifier': 'hello-message',
+        'long_name': 'Hello Message',
+        'version':     [2021, 11, 10],
+    }],
+    'generated_by': expected_generated_by
+}
+
+expected = [expected_mapping, *expected_resources, expected_source_description]
+expected_items = expected[:3]
+
+def run_reuse(command, **kwargs):
+    """
+    Instead of running a 'reuse' command, check if 'mock_reuse_missing' file
+    exists under root directory. If yes, raise FileNotFoundError as if 'reuse'
+    command was missing. If not, check if 'README.txt.license' file exists
+    in the requested directory and return zero if it does.
+    """
+    expected = ['reuse', '--root', '<root>',
+                'lint' if 'lint' in command else 'spdx']
+
+    root_path = Path(process_command(command, expected)['root'])
+
+    if (root_path / 'mock_reuse_missing').exists():
+        raise FileNotFoundError('dummy')
+
+    is_reuse_compliant = (root_path / 'README.txt.license').exists()
+
+    return MockedCompletedProcess(command, 1 - is_reuse_compliant,
+                                  stdout=f'dummy {expected[-1]} output',
+                                  text_output=kwargs.get('text'))
+
+mocked_piggybacked_archives = [
+    PurePosixPath('apt/something.deb'),
+    PurePosixPath('apt/something.orig.tar.gz'),
+    PurePosixPath('apt/something.debian.tar.xz'),
+    PurePosixPath('othersystem/other-something.tar.gz')
+]
+
+@pytest.fixture
+def mock_piggybacked_apt_system(monkeypatch):
+    """Make local_apt.piggybacked_system() return a mocked result."""
+    # We set 'td' to a temporary dir path further below.
+    td = None
+
+    class MockedPiggybacked:
+        """Minimal mock of Piggybacked object."""
+        package_license_files = [PurePosixPath('.apt-root/.../copyright')]
+        resource_must_depend = [{'identifier': 'apt-common-licenses'}]
+
+        def resolve_file(path):
+            """
+            For each path that starts with '.apt-root' return a valid dummy file
+            path.
+            """
+            if path.parts[0] != '.apt-root':
+                return None
+
+            (td / path.name).write_text(f'dummy {path.name}')
+
+            return (td / path.name)
+
+        def archive_files():
+            """Yield some valid dummy file path tuples."""
+            for desired_path in mocked_piggybacked_archives:
+                real_path = td / desired_path.name
+                real_path.write_text(f'dummy {desired_path.name}')
+
+                yield desired_path, real_path
+
+    @contextmanager
+    def mocked_piggybacked_system(piggyback_def, piggyback_files):
+        """Mock the execution of local_apt.piggybacked_system()."""
+        assert piggyback_def == {
+	    'system': 'apt',
+	    'distribution': 'nabia',
+	    'packages': ['somelib=1.0'],
+	    'dependencies': False
+        }
+        if piggyback_files is not None:
+            assert {str(path) for path in mocked_piggybacked_archives} == \
+                {path.relative_to(piggyback_files).as_posix()
+                 for path in piggyback_files.rglob('*') if path.is_file()}
+
+        yield MockedPiggybacked
+
+    monkeypatch.setattr(local_apt, 'piggybacked_system',
+                        mocked_piggybacked_system)
+
+    with TemporaryDirectory() as td:
+        td = Path(td)
+        yield
+
+@pytest.fixture
+def sample_source():
+    """Prepare a directory with sample Haketilo source package."""
+    with TemporaryDirectory() as td:
+        sample_source = Path(td) / 'hello'
+        for name, contents in src_files.items():
+            path = sample_source / name
+            path.parent.mkdir(parents=True, exist_ok=True)
+            path.write_bytes(contents)
+
+        yield sample_source
+
+def collect(list):
+    """Decorate function by appending it to the specified list."""
+    def decorator(function):
+        """The actual decorator that will be applied."""
+        list.append(function)
+        return function
+
+    return decorator
+
+variant_makers = []
+
+@collect(variant_makers)
+def sample_source_change_index_json(monkeypatch, sample_source):
+    """
+    Return a non-standard path for index.json. Ensure parent directories exist.
+    """
+    # Use a path under sample_source so that it gets auto-deleted after the
+    # test. Use a file under .git because .git is ignored by REUSE.
+    path = sample_source / '.git' / 'replacement.json'
+    path.parent.mkdir()
+    return path
+
+@collect(variant_makers)
+def sample_source_add_comments(monkeypatch, sample_source):
+    """Add index.json comments that should be preserved."""
+    for dictionary in index_obj, *index_obj['definitions'], *expected:
+        monkeypatch.setitem(dictionary, 'comment', 'index.json comment')
+
+@collect(variant_makers)
+def sample_source_remove_spdx(monkeypatch, sample_source):
+    """Remove spdx report generation."""
+    monkeypatch.delitem(index_obj, 'reuse_generate_spdx_report')
+
+    pred = lambda ref: ref['file'] != 'report.spdx'
+    copy_refs_in = list(filter(pred, index_obj['copyright']))
+    monkeypatch.setitem(index_obj, 'copyright', copy_refs_in)
+
+    copy_refs_out = list(filter(pred, expected_source_copyright))
+    for obj in expected:
+        monkeypatch.setitem(obj, 'source_copyright', copy_refs_out)
+
+    monkeypatch.delitem(dist_files, 'report.spdx')
+
+    # To verify that reuse does not get called now, make mocked subprocess.run()
+    # raise an error if called.
+    (sample_source / 'mock_reuse_missing').touch()
+
+@collect(variant_makers)
+def sample_source_remove_additional_files(monkeypatch, sample_source):
+    """Use default value ([]) for 'additionall_files' property."""
+    monkeypatch.delitem(index_obj, 'additional_files')
+
+    for name in 'README.txt', 'README.txt.license', '.reuse/dep5':
+        monkeypatch.delitem(src_files, name)
+
+@collect(variant_makers)
+def sample_source_remove_script(monkeypatch, sample_source):
+    """Use default value ([]) for 'scripts' property in one of the resources."""
+    monkeypatch.delitem(index_obj['definitions'][2], 'scripts')
+
+    monkeypatch.setitem(expected_resources[1], 'scripts', [])
+
+    for files in dist_files, src_files:
+        monkeypatch.delitem(files, 'message.js')
+
+@collect(variant_makers)
+def sample_source_remove_payloads(monkeypatch, sample_source):
+    """Use default value ({}) for 'payloads' property in mapping."""
+    monkeypatch.delitem(index_obj['definitions'][0], 'payloads')
+
+    monkeypatch.setitem(expected_mapping, 'payloads', {})
+
+@collect(variant_makers)
+def sample_source_remove_uuids(monkeypatch, sample_source):
+    """Don't use UUIDs (they are optional)."""
+    for definition in index_obj['definitions']:
+        monkeypatch.delitem(definition, 'uuid')
+
+    for description in expected:
+        if 'uuid' in description:
+            monkeypatch.delitem(description, 'uuid')
+
+@collect(variant_makers)
+def sample_source_add_extra_props(monkeypatch, sample_source):
+    """Add some unrecognized properties that should be stripped."""
+    to_process = [index_obj]
+    while to_process:
+        processed = to_process.pop()
+
+        if type(processed) is list:
+            to_process.extend(processed)
+        elif type(processed) is dict and 'spurious_property' not in processed:
+            to_process.extend(v for k, v in processed.items()
+                              if k != 'payloads')
+            monkeypatch.setitem(processed, 'spurious_property', 'some_value')
+
+@collect(variant_makers)
+def sample_source_make_version_2(monkeypatch, sample_source,
+                                 expected_documents_to_modify=[]):
+    """Increase sources' schema version from 1 to 2."""
+    for obj in index_obj, *expected_documents_to_modify:
+        monkeypatch.setitem(obj, '$schema', obj['$schema'].replace('1', '2'))
+
+permission_variant_makers = []
+
+@collect(permission_variant_makers)
+def sample_source_bool_perm_ignored(permission, monkeypatch, sample_source,
+                                    value=True):
+    """
+    Specify a boolean permissions in sources, but keep sources' schema version
+    at 1.
+    """
+    for definition in index_obj['definitions']:
+        monkeypatch.setitem(definition, 'permissions', {permission: value})
+
+@collect(permission_variant_makers)
+def sample_source_bool_perm(permission, monkeypatch, sample_source):
+    """Specify a boolean permission in sources."""
+    sample_source_bool_perm_ignored(permission, monkeypatch, sample_source)
+    sample_source_make_version_2(monkeypatch, sample_source, expected_items)
+
+    for obj in expected_items:
+        monkeypatch.setitem(obj, 'permissions', {permission: True})
+
+@collect(permission_variant_makers)
+def sample_source_bool_perm_defaults(permission, monkeypatch, sample_source):
+    """
+    Specify a boolean permission in sources but use the default value ("False").
+    """
+    sample_source_bool_perm_ignored(permission, monkeypatch, sample_source,
+                                    value=False)
+    sample_source_make_version_2(monkeypatch, sample_source)
+
+for permission in 'cors_bypass', 'eval':
+    for variant_maker in permission_variant_makers:
+        variant_makers.append(ft.partial(variant_maker, permission))
+
+@collect(variant_makers)
+def sample_source_req_mappings_ignored(monkeypatch, sample_source,
+                                       value=[{'identifier': 'mapping-dep'}]):
+    """
+    Specify dependencies on mappings, but keep sources' schema version at 1.
+    """
+    for definition in index_obj['definitions']:
+        monkeypatch.setitem(definition, 'required_mappings', value);
+
+@collect(variant_makers)
+def sample_source_req_mappings(monkeypatch, sample_source):
+    """Specify dependencies on mappings."""
+    sample_source_req_mappings_ignored(monkeypatch, sample_source)
+    sample_source_make_version_2(monkeypatch, sample_source, expected_items)
+
+    for obj in expected_items:
+        monkeypatch.setitem(obj, 'required_mappings',
+                            [{'identifier': 'mapping-dep'}])
+
+@collect(variant_makers)
+def sample_source_req_mappings_defaults(monkeypatch, sample_source):
+    """Specify dependencies of a mapping, but use the default value ("[]")."""
+    sample_source_req_mappings_ignored(monkeypatch, sample_source, value=[])
+    sample_source_make_version_2(monkeypatch, sample_source)
+
+@collect(variant_makers)
+def sample_source_combined_def(monkeypatch, sample_source):
+    """Define mapping and resource together."""
+    sample_source_make_version_2(monkeypatch, sample_source)
+
+    mapping_def   = index_obj['definitions'][0]
+    resource_defs = index_obj['definitions'][1:3]
+
+    item_defs_shortened = [mapping_def, resource_defs[1]]
+    monkeypatch.setitem(index_obj, 'definitions', item_defs_shortened)
+
+    monkeypatch.setitem(mapping_def, 'type', 'mapping_and_resource')
+
+    new_mapping_ver = [*expected_mapping['version'], 1]
+    monkeypatch.setitem(mapping_def, 'revision', 1)
+    monkeypatch.setitem(expected_mapping, 'version', new_mapping_ver)
+
+    for prop in 'scripts', 'dependencies':
+        monkeypatch.setitem(mapping_def, prop, resource_defs[0][prop])
+
+    monkeypatch.setitem(expected_resources[0], 'uuid', mapping_def['uuid'])
+    monkeypatch.setitem(expected_resources[0], 'description',
+                        mapping_def['description'])
+
+    monkeypatch.setitem(expected_source_description['definitions'][0],
+                        'version', new_mapping_ver)
+
+@collect(variant_makers)
+def sample_source_minmax_haketilo_ver_ignored(monkeypatch, sample_source,
+                                              min_ver=[1, 2], max_ver=[1, 2]):
+    """
+    Specify version constraints on Haketilo, but keep sources' schema version at
+    1.
+    """
+    mapping_def = index_obj['definitions'][0]
+    monkeypatch.setitem(mapping_def, 'min_haketilo_version', min_ver)
+    monkeypatch.setitem(mapping_def, 'max_haketilo_version', max_ver)
+
+@collect(variant_makers)
+def sample_source_minmax_haketilo_ver(monkeypatch, sample_source):
+    """Specify version constraints on Haketilo."""
+    sample_source_minmax_haketilo_ver_ignored(monkeypatch, sample_source)
+    sample_source_make_version_2(monkeypatch, sample_source, [expected_mapping])
+
+    monkeypatch.setitem(expected_mapping, 'min_haketilo_version', [1, 2])
+    monkeypatch.setitem(expected_mapping, 'max_haketilo_version', [1, 2])
+
+@collect(variant_makers)
+def sample_source_minmax_haketilo_ver_default(monkeypatch, sample_source):
+    """Specify version constraints on Haketilo, but use default values."""
+    sample_source_minmax_haketilo_ver_ignored(monkeypatch, sample_source,
+                                              min_ver=[1], max_ver=[65536])
+    sample_source_make_version_2(monkeypatch, sample_source)
+
+piggyback_archive_names = [
+    'apt/something.deb',
+    'apt/something.orig.tar.gz',
+    'apt/something.debian.tar.xz',
+    'othersystem/other-something.tar.gz'
+]
+
+@collect(variant_makers)
+def sample_source_add_piggyback_ignored(monkeypatch, sample_source,
+                                        extra_build_args={}):
+    """
+    Add piggybacked foreign system packages, but keep sources' schema version at
+    1.
+    """
+    old_build = build.Build
+    new_build = lambda *a, **kwa: old_build(*a, **kwa, **extra_build_args)
+    monkeypatch.setattr(build, 'Build', new_build)
+
+    monkeypatch.setitem(index_obj, 'piggyback_on', {
+	'system': 'apt',
+	'distribution': 'nabia',
+	'packages': ['somelib=1.0'],
+	'dependencies': False
+    })
+
+@collect(variant_makers)
+def sample_source_add_piggyback(monkeypatch, sample_source,
+                                extra_build_args={}):
+    """Add piggybacked foreign system packages."""
+    sample_source_add_piggyback_ignored\
+        (monkeypatch, sample_source, extra_build_args)
+
+    sample_source_make_version_2(monkeypatch, sample_source)
+
+    new_refs = {}
+    for name in '.apt-root/.../copyright', '.apt-root/.../script.js':
+        contents = f'dummy {PurePosixPath(name).name}'.encode()
+        digest = sha256(contents).digest().hex()
+        monkeypatch.setitem(dist_files, name, contents)
+        monkeypatch.setitem(sha256_hashes, name, digest)
+        new_refs[PurePosixPath(name).name] = {'file': name, 'sha256': digest}
+
+    new_list = [*expected_source_copyright, new_refs['copyright']]
+    for obj in expected:
+        monkeypatch.setitem(obj, 'source_copyright', new_list)
+
+    for obj in expected_resources:
+        new_list = [{'identifier': 'apt-common-licenses'}, *obj['dependencies']]
+        monkeypatch.setitem(obj, 'dependencies', new_list)
+
+    for obj in index_obj['definitions'][1], expected_resources[0]:
+        new_list = [new_refs['script.js'], *obj['scripts']]
+        monkeypatch.setitem(obj, 'scripts', new_list)
+
+    for name in piggyback_archive_names:
+        path = PurePosixPath('hello.foreign-packages') / name
+        monkeypatch.setitem(extra_archive_files, str(path),
+                            f'dummy {path.name}'.encode())
+
+def prepare_foreign_packages_dir(path):
+    """
+    Put some dummy archive in the directory so that it can be passed to
+    piggybacked_system().
+    """
+    for name in piggyback_archive_names:
+        archive_path = path / name
+        archive_path.parent.mkdir(parents=True, exist_ok=True)
+        archive_path.write_text(f'dummy {archive_path.name}')
+
+@collect(variant_makers)
+def sample_source_add_piggyback_pass_archives(monkeypatch, sample_source):
+    """
+    Add piggybacked foreign system packages, use pre-downloaded foreign package
+    archives (have Build() find them in their default directory).
+    """
+    # Dir next to 'sample_source' will also be gc'd by sample_source() fixture.
+    foreign_packages_dir = sample_source.parent / 'arbitrary-name'
+
+    prepare_foreign_packages_dir(foreign_packages_dir)
+
+    sample_source_add_piggyback(monkeypatch, sample_source,
+                                {'piggyback_files': foreign_packages_dir})
+
+@collect(variant_makers)
+def sample_source_add_piggyback_find_archives(monkeypatch, sample_source):
+    """
+    Add piggybacked foreign system packages, use pre-downloaded foreign package
+    archives (specify their directory as argument to Build()).
+    """
+    # Dir next to 'sample_source' will also be gc'd by sample_source() fixture.
+    foreign_packages_dir = sample_source.parent / 'hello.foreign-packages'
+
+    prepare_foreign_packages_dir(foreign_packages_dir)
+
+    sample_source_add_piggyback(monkeypatch, sample_source)
+
+@collect(variant_makers)
+def sample_source_add_piggyback_no_download(monkeypatch, sample_source,
+                                            pass_directory_to_build=False):
+    """
+    Add piggybacked foreign system packages, use pre-downloaded foreign package
+    archives.
+    """
+    # Use a dir next to 'sample_source'; have it gc'd by sample_source fixture.
+    if pass_directory_to_build:
+        foreign_packages_dir = sample_source.parent / 'arbitrary-name'
+    else:
+        foreign_packages_dir = sample_source.parent / 'hello.foreign-packages'
+
+    prepare_foreign_packages_dir(foreign_packages_dir)
+
+    sample_source_add_piggyback(monkeypatch, sample_source)
+
+@pytest.fixture(params=[lambda m, s: None, *variant_makers])
+def sample_source_make_variants(request, monkeypatch, sample_source,
+                                mock_piggybacked_apt_system):
+    """
+    Prepare a directory with sample Haketilo source package in multiple slightly
+    different versions (all correct). Return an index.json path that should be
+    used when performing test build.
+    """
+    index_path = request.param(monkeypatch, sample_source) or Path('index.json')
+
+    index_text = json.dumps(index_obj)
+
+    (sample_source / index_path).write_text(index_text)
+
+    monkeypatch.setitem(src_files, 'index.json', index_text.encode())
+
+    return index_path
+
+def try_validate(as_what, instance):
+    """
+    Select the right JSON schema. Return without errors only if the instance
+    validates against it.
+    """
+    schema_fmt = f'{as_what}-{{}}.schema.json'
+    json_instances.validate_instance(instance, schema_fmt)
+
+@pytest.mark.subprocess_run(build, run_reuse)
+@pytest.mark.usefixtures('mock_subprocess_run')
+def test_build(sample_source, sample_source_make_variants, tmpdir):
+    """Build the sample source package and verify the produced files."""
+    index_json_path = sample_source_make_variants
+
+    # First, build the package
+    build.Build(sample_source, index_json_path).write_package_files(tmpdir)
+
+    # Verify directories under destination directory
+    assert {'file', 'resource', 'mapping', 'source'} == \
+        set([path.name for path in tmpdir.iterdir()])
+
+    # Verify files under 'file/'
+    file_dir = tmpdir / 'file' / 'sha256'
+
+    for name, contents in dist_files.items():
+        dist_file_path = file_dir / sha256_hashes[name]
+        assert dist_file_path.is_file()
+        assert dist_file_path.read_bytes() == contents
+
+    assert {p.name for p in file_dir.iterdir()} == \
+        {sha256_hashes[name] for name in dist_files.keys()}
+
+    # Verify files under 'resource/'
+    resource_dir = tmpdir / 'resource'
+
+    assert {rj['identifier'] for rj in expected_resources} == \
+        {path.name for path in resource_dir.iterdir()}
+
+    for resource_json in expected_resources:
+        subdir = resource_dir / resource_json['identifier']
+        ver_str = versions.version_string(resource_json['version'])
+        assert [ver_str] == [path.name for path in subdir.iterdir()]
+
+        assert json.loads((subdir / ver_str).read_text()) == resource_json
+
+        try_validate('api_resource_description', resource_json)
+
+    # Verify files under 'mapping/'
+    mapping_dir = tmpdir / 'mapping'
+    assert ['helloapple'] == [path.name for path in mapping_dir.iterdir()]
+
+    subdir = mapping_dir / 'helloapple'
+
+    ver_str = versions.version_string(expected_mapping['version'])
+    assert [ver_str] == [path.name for path in subdir.iterdir()]
+
+    assert json.loads((subdir / ver_str).read_text()) == expected_mapping
+
+    try_validate('api_mapping_description', expected_mapping)
+
+    # Verify files under 'source/'
+    source_dir = tmpdir / 'source'
+    assert {'hello.json', 'hello.zip'} == \
+        {path.name for path in source_dir.iterdir()}
+
+    archive_files = {**dict((f'hello/{name}', contents)
+                            for name, contents in src_files.items()),
+                     **extra_archive_files}
+
+    with ZipFile(source_dir / 'hello.zip', 'r') as archive:
+        print(archive.namelist())
+        assert len(archive.namelist()) == len(archive_files)
+
+        for name, contents in archive_files.items():
+            assert archive.read(name) == contents
+
+    zip_ref = expected_source_description['source_archives']['zip']
+    zip_contents = (source_dir / 'hello.zip').read_bytes()
+    zip_ref['sha256'] = sha256(zip_contents).digest().hex()
+
+    assert json.loads((source_dir / 'hello.json').read_text()) == \
+        expected_source_description
+
+    try_validate('api_source_description', expected_source_description)
+
+error_makers = []
+
+@collect(error_makers)
+def sample_source_error_missing_file(monkeypatch, sample_source):
+    """
+    Modify index.json to expect missing report.spdx file and cause an error.
+    """
+    monkeypatch.delitem(index_obj, 'reuse_generate_spdx_report')
+    return FileReferenceError, '^referenced_file_report.spdx_missing$'
+
+@collect(error_makers)
+def sample_source_error_index_schema(monkeypatch, sample_source):
+    """Modify index.json to be incompliant with the schema."""
+    monkeypatch.delitem(index_obj, 'definitions')
+    return ValidationError,
+
+@collect(error_makers)
+def sample_source_error_unknown_index_schema(monkeypatch, sample_source):
+    """Modify index.json to be use a not-yet-released schema."""
+    schema_id = \
+        'https://hydrilla.koszko.org/schemas/package_source-65536.schema.json'
+    monkeypatch.setitem(index_obj, "$schema", schema_id)
+    return hydrilla_util.UnknownSchemaError, \
+        r'^unknown_schema_package_source_.*/hello/index\.json$'
+
+@collect(error_makers)
+def sample_source_error_bad_comment(monkeypatch, sample_source):
+    """Modify index.json to have an invalid '/' in it."""
+    return json.JSONDecodeError, '^bad_comment: .*', \
+        json.dumps(index_obj) + '/something\n'
+
+@collect(error_makers)
+def sample_source_error_bad_json(monkeypatch, sample_source):
+    """Modify index.json to not be valid json even after comment stripping."""
+    return json.JSONDecodeError, '', json.dumps(index_obj) + '???\n'
+
+@collect(error_makers)
+def sample_source_error_missing_reuse(monkeypatch, sample_source):
+    """Cause mocked reuse process invocation to fail with FileNotFoundError."""
+    (sample_source / 'mock_reuse_missing').touch()
+    return build.ReuseError, '^couldnt_execute_reuse_is_it_installed$'
+
+@collect(error_makers)
+def sample_source_error_missing_license(monkeypatch, sample_source):
+    """Remove a file to make package REUSE-incompliant."""
+    (sample_source / 'README.txt.license').unlink()
+
+    error_regex = """^\
+command_reuse --root \\S+ lint_failed
+
+STDOUT_OUTPUT_heading
+
+dummy lint output
+
+STDERR_OUTPUT_heading
+
+some error output\
+$\
+"""
+
+    return build.ReuseError, error_regex
+
+@collect(error_makers)
+def sample_source_error_file_outside(monkeypatch, sample_source):
+    """Make index.json illegally reference a file outside srcdir."""
+    new_list = [*index_obj['copyright'], {'file': '../abc'}]
+    monkeypatch.setitem(index_obj, 'copyright', new_list)
+    return FileReferenceError, '^path_contains_double_dot_\\.\\./abc$'
+
+@collect(error_makers)
+def sample_source_error_reference_itself(monkeypatch, sample_source):
+    """Make index.json illegally reference index.json."""
+    new_list = [*index_obj['copyright'], {'file': 'index.json'}]
+    monkeypatch.setitem(index_obj, 'copyright', new_list)
+    return FileReferenceError, '^loading_reserved_index_json$'
+
+@collect(error_makers)
+def sample_source_error_report_excluded(monkeypatch, sample_source):
+    """
+    Make index.json require generation of report.spdx but don't include it among
+    copyright files.
+    """
+    new_list = [file_ref for file_ref in index_obj['copyright']
+                if file_ref['file'] != 'report.spdx']
+    monkeypatch.setitem(index_obj, 'copyright', new_list)
+    return FileReferenceError, '^report_spdx_not_in_copyright_list$'
+
+@collect(error_makers)
+def sample_source_error_combined_unsupported(monkeypatch, sample_source):
+    """
+    Define mapping and resource together but leave source schema version at 1.x
+    where this is unsupported.
+    """
+    mapping_def = index_obj['definitions'][0]
+    monkeypatch.setitem(mapping_def, 'type', 'mapping_and_resource')
+
+    return ValidationError,
+
+@pytest.fixture(params=error_makers)
+def sample_source_make_errors(request, monkeypatch, sample_source):
+    """
+    Prepare a directory with sample Haketilo source package in multiple slightly
+    broken versions. Return an error type that should be raised when running
+    test build.
+    """
+    error_type, error_regex, index_text = \
+        [*request.param(monkeypatch, sample_source), '', ''][0:3]
+
+    index_text = index_text or json.dumps(index_obj)
+
+    (sample_source / 'index.json').write_text(index_text)
+
+    monkeypatch.setitem(src_files, 'index.json', index_text.encode())
+
+    return error_type, error_regex
+
+@pytest.mark.subprocess_run(build, run_reuse)
+@pytest.mark.usefixtures('mock_subprocess_run')
+def test_build_error(tmpdir, sample_source, sample_source_make_errors):
+    """Try building the sample source package and verify generated errors."""
+    error_type, error_regex = sample_source_make_errors
+
+    dstdir = Path(tmpdir) / 'dstdir'
+    dstdir.mkdir(exist_ok=True)
+
+    with pytest.raises(error_type, match=error_regex):
+        build.Build(sample_source, Path('index.json'))\
+             .write_package_files(dstdir)
diff --git a/tests/test_item_infos.py b/tests/test_item_infos.py
new file mode 100644
index 0000000..9de3c96
--- /dev/null
+++ b/tests/test_item_infos.py
@@ -0,0 +1,527 @@
+# SPDX-License-Identifier: CC0-1.0
+
+# Copyright (C) 2022 Wojtek Kosior <koszko@koszko.org>
+#
+# Available under the terms of Creative Commons Zero v1.0 Universal.
+
+import pytest
+import pathlib
+import re
+import dataclasses as dc
+
+from immutables import Map
+
+from hydrilla import item_infos, versions, json_instances
+from hydrilla.exceptions import HaketiloException
+
+def test_make_item_refs_seq_empty():
+    """...."""
+    assert item_infos.make_item_refs_seq([]) == ()
+
+def test_get_item_refs_seq_nonempty():
+    """...."""
+    ref_objs = [{'identifier': 'abc'}, {'identifier': 'def'}]
+
+    result = item_infos.make_item_refs_seq(ref_objs)
+
+    assert type(result) is tuple
+    assert [ref.identifier for ref in result] == ['abc', 'def']
+
+@pytest.fixture
+def mock_make_item_refs_seq(monkeypatch):
+    """...."""
+    def mocked_make_item_refs_seq(ref_objs):
+        """...."""
+        assert ref_objs == getattr(
+            mocked_make_item_refs_seq,
+            'expected',
+            [{'identifier': 'abc'}, {'identifier': 'def'}]
+        )
+
+        return (item_infos.ItemRef('abc'), item_infos.ItemRef('def'))
+
+    monkeypatch.setattr(item_infos, 'make_item_refs_seq',
+                        mocked_make_item_refs_seq)
+
+    return mocked_make_item_refs_seq
+
+def test_make_required_mappings_compat_too_low():
+    """...."""
+    assert item_infos.make_required_mappings('whatever', 1) == ()
+
+@pytest.mark.usefixtures('mock_make_item_refs_seq')
+def test_make_required_mappings_compat_ok():
+    """...."""
+    ref_objs = [{'identifier': 'abc'}, {'identifier': 'def'}]
+
+    assert item_infos.make_required_mappings(ref_objs, 2) == \
+        (item_infos.ItemRef('abc'), item_infos.ItemRef('def'))
+
+def test_make_file_refs_seq_empty():
+    """...."""
+    assert item_infos.make_file_refs_seq([]) == ()
+
+def test_make_file_refs_seq_nonempty():
+    """...."""
+    ref_objs = [{'file': 'abc', 'sha256': 'dummy_hash1'},
+                {'file': 'def', 'sha256': 'dummy_hash2'}]
+
+    result = item_infos.make_file_refs_seq(ref_objs)
+
+    assert type(result) is tuple
+    assert [ref.name for ref in result]   == ['abc', 'def']
+    assert [ref.sha256 for ref in result] == ['dummy_hash1', 'dummy_hash2']
+
+def test_generated_by_make_empty():
+    """...."""
+    assert item_infos.GeneratedBy.make(None) == None
+
+@pytest.mark.parametrize('_in, out_version', [
+    ({'name': 'abc'},                     None),
+    ({'name': 'abc', 'version': '1.1.1'}, '1.1.1')
+])
+def test_generated_by_make_nonempty(_in, out_version):
+    """...."""
+    generated_by = item_infos.GeneratedBy.make(_in)
+
+    assert generated_by.name    == 'abc'
+    assert generated_by.version == out_version
+
+def test_load_item_info(monkeypatch):
+    """...."""
+    def mocked_read_instance(instance_or_path):
+        """...."""
+        assert instance_or_path == 'dummy_path'
+        return 'dummy_instance'
+
+    monkeypatch.setattr(json_instances, 'read_instance', mocked_read_instance)
+
+    def mocked_validate_instance(instance, schema_fmt):
+        """...."""
+        assert instance == 'dummy_instance'
+        assert schema_fmt == 'api_exotictype_description-{}.schema.json'
+        return 7
+
+    monkeypatch.setattr(json_instances, 'validate_instance',
+                        mocked_validate_instance)
+
+    class MockedLoadedType:
+        """...."""
+        def make(instance, schema_compat, repository):
+            """...."""
+            assert instance      == 'dummy_instance'
+            assert schema_compat == 7
+            assert repository    == 'somerepo'
+            return 'dummy_item_info'
+
+        type_name = 'exotictype'
+
+    assert item_infos._load_item_info(
+        MockedLoadedType,
+        'dummy_path',
+        'somerepo'
+    ) == 'dummy_item_info'
+
+def test_make_payloads(monkeypatch):
+    """...."""
+    payloads_obj = {'http*://example.com/': {'identifier': 'someresource'}}
+
+    def mocked_parse_pattern(pattern):
+        """...."""
+        assert pattern == 'http*://example.com/'
+
+        yield 'dummy_parsed_pattern_1'
+        yield 'dummy_parsed_pattern_2'
+
+    monkeypatch.setattr(item_infos, 'parse_pattern', mocked_parse_pattern)
+
+    assert item_infos.make_payloads(payloads_obj) == Map({
+        'dummy_parsed_pattern_1': item_infos.ItemRef('someresource'),
+        'dummy_parsed_pattern_2': item_infos.ItemRef('someresource')
+    })
+
+@pytest.mark.parametrize('info_mod, in_mod', [
+    ({},                     {}),
+    ({'uuid': 'dummy_uuid'}, {}),
+    ({},                     {'uuid': 'dummy_uuid'}),
+    ({'uuid': 'dummy_uuid'}, {'uuid': 'dummy_uuid'}),
+    ({},                     {'identifier': 'abc', '_initialized': True}),
+    ({},                     {'_by_version': Map({(1, 2): 'dummy_old_info'})})
+])
+def test_versioned_item_info_register(info_mod, in_mod):
+    """...."""
+    class DummyInfo:
+        """...."""
+        uuid       = None
+        identifier = 'abc'
+        version    = (1, 2)
+
+    for name, value in info_mod.items():
+        setattr(DummyInfo, name, value)
+
+    in_fields = {
+        'uuid':         None,
+        'identifier':   '<dummy>',
+        '_by_version':  Map(),
+        '_initialized': False,
+        **in_mod
+    }
+    out_fields = {
+        'uuid':         DummyInfo.uuid or in_mod.get('uuid'),
+        'identifier':   DummyInfo.identifier,
+        '_by_version':  Map({(1, 2): DummyInfo}),
+        '_initialized': True
+    }
+
+    versioned     = item_infos.VersionedItemInfo(**in_fields)
+    new_versioned = versioned.register(DummyInfo)
+
+    assert dc.asdict(versioned)     == in_fields
+    assert dc.asdict(new_versioned) == out_fields
+
+def test_versioned_item_info_register_bad_uuid():
+    """...."""
+    versioned = item_infos.VersionedItemInfo(
+        identifier='abc',
+        uuid='old_uuid'
+    )
+
+    class DummyInfo:
+        """...."""
+        uuid       = 'new_uuid'
+        identifier = 'abc'
+        version    = (1, 2)
+
+    with pytest.raises(HaketiloException, match='^uuid_mismatch_abc$'):
+        versioned.register(DummyInfo)
+
+@pytest.mark.parametrize('previous_registrations', [
+    Map(),
+    Map({(1, 2): 'dummy_info'})
+])
+def test_versioned_item_info_unregister(previous_registrations):
+    """...."""
+    versioned = item_infos.VersionedItemInfo(
+        identifier  = 'abc',
+        _by_version = previous_registrations
+    )
+
+    assert versioned.unregister((1, 2)) == \
+        dc.replace(versioned, _by_version=Map())
+
+@pytest.mark.parametrize('registrations, out', [
+    (Map(),                       True),
+    (Map({(1, 2): 'dummy_info'}), False)
+])
+def test_versioned_item_info_is_empty(registrations, out):
+    """...."""
+    versioned = item_infos.VersionedItemInfo(
+        identifier  = 'abc',
+        _by_version = registrations
+    )
+
+    assert versioned.is_empty() == out
+
+@pytest.mark.parametrize('versions, out', [
+    ([(1, 2), (1, 2, 1), (0, 9999, 4), (1, 0, 2)],    (1, 2, 1)),
+    ([(1, 2)],                                        (1, 2))
+])
+def test_versioned_item_info_newest_version(versions, out):
+    """...."""
+    versioned = item_infos.VersionedItemInfo(
+        identifier  = 'abc',
+        _by_version = Map((ver, 'dummy_info') for ver in versions)
+    )
+
+    assert versioned.newest_version() == out
+
+def test_versioned_item_info_newest_version_bad(monkeypatch):
+    """...."""
+    monkeypatch.setattr(item_infos.VersionedItemInfo, 'newest_version',
+                        lambda self: 'dummy_ver1')
+
+    versioned = item_infos.VersionedItemInfo(
+        identifier  = 'abc',
+        _by_version = Map(dummy_ver1='dummy_info1', dummy_ver2='dummy_info2')
+    )
+
+    assert versioned.get_newest() == 'dummy_info1'
+
+def test_versioned_item_info_get_by_ver():
+    """...."""
+    versioned = item_infos.VersionedItemInfo(
+        identifier  = 'abc',
+        _by_version = Map({(1, 2): 'dummy_info1', (3, 4, 5): 'dummy_info2'})
+    )
+
+    assert versioned.get_by_ver(range(1, 3)) == 'dummy_info1'
+
+@pytest.mark.parametrize('versions, out', [
+    ([(1, 2), (0, 999, 4), (1, 0, 2)], ['(0, 999, 4)', '(1, 0, 2)', '(1, 2)']),
+    ([],                               [])
+])
+def test_versioned_item_get_all(versions, out):
+    """...."""
+    versioned = item_infos.VersionedItemInfo(
+        identifier  = 'abc',
+        _by_version = Map((ver, str(ver)) for ver in versions)
+    )
+
+    assert [*versioned.get_all()] == out
+
+sample_resource_obj = {
+    'source_name':       'somesource',
+    'source_copyright':  [{'file': 'ABC', 'sha256': 'dummy_sha256'}],
+    'version':           [1, 2, 3, 0],
+    'identifier':        'someid',
+    'uuid':              None,
+    'long_name':         'Some Thing',
+    'required_mappings': [{'identifier': 'required1'}],
+    'generated_by':      {'name': 'sometool', 'version': '1.1.1'},
+    'revision':          4,
+    'dependencies':      [{'identifier': 'abc'}, {'identifier': 'def'}],
+    'scripts':           [{'file': 'ABC', 'sha256': 'dummy_sha256'}]
+}
+
+sample_mapping_obj = {
+    **sample_resource_obj,
+    'payloads': {
+        'https://example.com/': {'identifier': 'someresource'}
+    }
+}
+
+del sample_mapping_obj['dependencies']
+del sample_mapping_obj['scripts']
+
+@pytest.fixture(scope='session')
+def sample_resource_info():
+    """...."""
+    return item_infos.ResourceInfo(
+        repository        = 'somerepo',
+        source_name       = 'somesource',
+        source_copyright  = (item_infos.FileRef('ABC', 'dummy_sha256'),),
+        version           = (1, 2, 3),
+        identifier        = 'someid',
+        uuid              = None,
+        long_name         = 'Some Thing',
+        required_mappings = (item_infos.ItemRef('required1'),),
+        generated_by      = item_infos.GeneratedBy('sometool', '1.1.1'),
+        revision          = 4,
+        dependencies      = (item_infos.ItemRef('abc'),
+                             item_infos.ItemRef('def')),
+        scripts           = (item_infos.FileRef('ABC', 'dummy_sha256'),)
+    )
+
+@pytest.fixture(scope='session')
+def sample_mapping_info():
+    """...."""
+    payloads = Map({'https://example.com/': item_infos.ItemRef('someresource')})
+
+    return item_infos.MappingInfo(
+        repository        = 'somerepo',
+        source_name       = 'somesource',
+        source_copyright  = (item_infos.FileRef('ABC', 'dummy_sha256'),),
+        version           = (1, 2, 3),
+        identifier        = 'someid',
+        uuid              = None,
+        long_name         = 'Some Thing',
+        required_mappings = (item_infos.ItemRef('required1'),),
+        generated_by      = item_infos.GeneratedBy('sometool', '1.1.1'),
+        payloads          = payloads
+    )
+
+@pytest.fixture(scope='session')
+def sample_info_base_init_kwargs(sample_resource_info):
+    kwargs = {}
+    for field_name in item_infos.ItemInfoBase.__annotations__.keys():
+        kwargs[field_name] = getattr(sample_resource_info, field_name)
+
+    return Map(kwargs)
+
+@pytest.fixture
+def mock_version_string(monkeypatch):
+    """...."""
+    def mocked_version_string(version, revision=None):
+        """...."""
+        assert version == (1, 2, 3)
+        assert revision in (None, 4)
+        return '1.2.3' if revision is None else '1.2.3-4'
+
+    monkeypatch.setattr(versions, 'version_string', mocked_version_string)
+
+@pytest.mark.usefixtures('mock_version_string')
+def test_item_info_path(sample_resource_info):
+    """...."""
+    assert sample_resource_info.path_relative_to_type() == 'someid/1.2.3'
+    assert sample_resource_info.path() == 'resource/someid/1.2.3'
+
+@pytest.mark.usefixtures('mock_version_string')
+def test_resource_info_versioned_identifier(sample_resource_info, monkeypatch):
+    """...."""
+    monkeypatch.setattr(item_infos.ItemInfoBase, 'versioned_identifier',
+                        lambda self: '<dummy>')
+
+    assert sample_resource_info.versioned_identifier == '<dummy>-4'
+
+@pytest.mark.usefixtures('mock_version_string')
+def test_mapping_info_versioned_identifier(sample_mapping_info):
+    """...."""
+    assert sample_mapping_info.versioned_identifier == 'someid-1.2.3'
+
+@pytest.fixture
+def mock_make_file_refs_seq(monkeypatch):
+    """...."""
+    def mocked_make_file_refs_seq(ref_objs):
+        """...."""
+        assert ref_objs == getattr(
+            mocked_make_file_refs_seq,
+            'expected',
+            [{'file': 'ABC', 'sha256': 'dummy_sha256'}]
+        )
+
+        return (item_infos.FileRef(name='ABC', sha256='dummy_sha256'),)
+
+    monkeypatch.setattr(item_infos, 'make_file_refs_seq',
+                        mocked_make_file_refs_seq)
+
+    return mocked_make_file_refs_seq
+
+@pytest.mark.parametrize('missing_prop', [
+    'required_mappings',
+    'generated_by',
+    'uuid'
+])
+@pytest.mark.usefixtures('mock_make_item_refs_seq', 'mock_make_file_refs_seq')
+def test_item_info_get_base_init_kwargs(
+        missing_prop,
+        monkeypatch,
+        sample_resource_info,
+        sample_info_base_init_kwargs,
+        mock_make_file_refs_seq
+):
+    """...."""
+    monkeypatch.delitem(sample_resource_obj, missing_prop)
+
+    def mocked_normalize_version(version):
+        """...."""
+        assert version == [1, 2, 3, 0]
+
+        return (1, 2, 3)
+
+    monkeypatch.setattr(versions, 'normalize_version', mocked_normalize_version)
+
+    def mocked_make_required_mappings(ref_objs, schema_compat):
+        """...."""
+        if missing_prop == 'required_mappings':
+            assert ref_objs == []
+        else:
+            assert ref_objs == [{'identifier': 'required1'}]
+
+        assert schema_compat == 2
+
+        return (item_infos.ItemRef('required1'),)
+
+    monkeypatch.setattr(item_infos, 'make_required_mappings',
+                        mocked_make_required_mappings)
+
+    def mocked_generated_by_make(generated_by_obj):
+        """...."""
+        if missing_prop == 'generated_by':
+            assert generated_by_obj == None
+        else:
+            assert generated_by_obj == {'name': 'sometool', 'version': '1.1.1'}
+
+        return item_infos.GeneratedBy(name='sometool', version='1.1.1')
+
+    monkeypatch.setattr(item_infos.GeneratedBy, 'make',
+                        mocked_generated_by_make)
+
+    expected = sample_info_base_init_kwargs
+    if missing_prop == 'uuid':
+        expected = expected.set('uuid', None)
+
+    Base = item_infos.ItemInfoBase
+    assert Base._get_base_init_kwargs(sample_resource_obj, 2, 'somerepo') == \
+        expected
+
+@pytest.fixture
+def mock_get_base_init_kwargs(monkeypatch, sample_info_base_init_kwargs):
+    """...."""
+    def mocked_get_base_init_kwargs(item_obj, schema_compat, repository):
+        """...."""
+        assert schema_compat          == 2
+        assert item_obj['identifier'] == 'someid'
+        assert repository             == 'somerepo'
+
+        return sample_info_base_init_kwargs
+
+    monkeypatch.setattr(item_infos.ItemInfoBase, '_get_base_init_kwargs',
+                        mocked_get_base_init_kwargs)
+
+@pytest.mark.parametrize('missing_prop', ['dependencies', 'scripts'])
+@pytest.mark.usefixtures('mock_get_base_init_kwargs')
+def test_resource_info_make(
+        missing_prop,
+        monkeypatch,
+        sample_resource_info,
+        mock_make_item_refs_seq,
+        mock_make_file_refs_seq
+):
+    """...."""
+    _in = sample_resource_obj
+    monkeypatch.delitem(_in, missing_prop)
+
+    if missing_prop == 'dependencies':
+        mock_make_item_refs_seq.expected = []
+    elif missing_prop == 'scripts':
+        mock_make_file_refs_seq.expected = []
+
+    assert item_infos.ResourceInfo.make(_in, 2, 'somerepo') == \
+        sample_resource_info
+
+@pytest.mark.parametrize('missing_payloads', [True, False])
+@pytest.mark.usefixtures('mock_get_base_init_kwargs', 'mock_make_item_refs_seq')
+def test_mapping_info_make(missing_payloads, monkeypatch, sample_mapping_info):
+    """...."""
+    _in = sample_mapping_obj
+    if missing_payloads:
+        monkeypatch.delitem(_in, 'payloads')
+
+    def mocked_make_payloads(payloads_obj):
+        """...."""
+        if missing_payloads:
+            assert payloads_obj == {}
+        else:
+            assert payloads_obj == \
+                {'https://example.com/': {'identifier': 'someresource'}}
+
+        return Map({'https://example.com/': item_infos.ItemRef('someresource')})
+
+    monkeypatch.setattr(item_infos, 'make_payloads', mocked_make_payloads)
+
+    assert item_infos.MappingInfo.make(_in, 2, 'somerepo') == \
+        sample_mapping_info
+
+@pytest.mark.parametrize('type_name', ['ResourceInfo', 'MappingInfo'])
+def test_make_item_info(type_name, monkeypatch):
+    """...."""
+    info_type = getattr(item_infos, type_name)
+
+    def mocked_load_item_info(_info_type, instance_or_path, repository):
+        """...."""
+        assert _info_type       == info_type
+        assert instance_or_path == 'dummy_path'
+        assert repository       == 'somerepo'
+        return 'dummy_info'
+
+    monkeypatch.setattr(item_infos, '_load_item_info', mocked_load_item_info)
+
+    assert info_type.load('dummy_path', 'somerepo') == 'dummy_info'
+
+def test_resource_info_hash(sample_resource_info):
+    """...."""
+    hash(sample_resource_info)
+
+def test_mapping_info_hash(sample_mapping_info):
+    """...."""
+    hash(sample_mapping_info)
diff --git a/tests/test_json_instances.py b/tests/test_json_instances.py
new file mode 100644
index 0000000..f5bd270
--- /dev/null
+++ b/tests/test_json_instances.py
@@ -0,0 +1,194 @@
+# SPDX-License-Identifier: CC0-1.0
+
+# Copyright (C) 2022 Wojtek Kosior <koszko@koszko.org>
+#
+# Available under the terms of Creative Commons Zero v1.0 Universal.
+
+import pytest
+import re
+
+from hydrilla import json_instances
+from hydrilla.exceptions import HaketiloException
+
+sample_json_no_comments = '{\n"so/me":\n"//json//"\n}\n'
+
+@pytest.mark.parametrize('_in', [
+    '{\n"so/me":\n"//json//"\n}\n',
+    '{//we\n"so/me"://will\n"//json//"//rock\n}//you\n'
+])
+def test_strip_json_comments(_in):
+    """...."""
+    assert json_instances.strip_json_comments(_in) == sample_json_no_comments
+
+@pytest.mark.parametrize('_in, line, char', [
+    ('/{\n"so/me":\n"//json//"\n}\n',                                 1, 1),
+    ('{\n"so/me":/\n"//json//"\n}/\n',                                2, 9),
+    ('{\n"so/me":/ huehue, I am an invalid comment\n"//json//"\n}\n', 2, 9)
+])
+def test_strip_json_comments_bad(_in, line, char):
+    """...."""
+    error_regex = f'^bad_json_comment_line_{line}_char_{char}$'
+    with pytest.raises(HaketiloException, match=error_regex):
+        json_instances.strip_json_comments(_in)
+
+@pytest.mark.parametrize('schema_name, full_schema_name', [
+    ('package_source-1.0.1.schema.json', 'package_source-1.0.1.schema.json'),
+    ('package_source-1.0.schema.json',   'package_source-1.0.1.schema.json'),
+    ('package_source-1.schema.json',     'package_source-1.0.1.schema.json'),
+    ('package_source-2.schema.json',     'package_source-2.schema.json')
+])
+def test_get_schema(schema_name, full_schema_name):
+    """...."""
+    url_prefix = 'https://hydrilla.koszko.org/schemas/'
+
+    for prefix in ('', url_prefix):
+        schema1 = json_instances._get_schema(prefix + schema_name)
+        assert schema1['$id'] == url_prefix + full_schema_name
+
+        schema2 = json_instances._get_schema(prefix + schema_name)
+        assert schema2 is schema1
+
+@pytest.mark.parametrize('_in', ['dummy_uri', {'$id': 'dummy_uri'}])
+def test_validator_for(_in, monkeypatch):
+    """...."""
+    def mocked_get_schema(schema_id):
+        """...."""
+        assert schema_id == 'dummy_uri'
+        return {'$id': 'dummy_uri'}
+
+    monkeypatch.setattr(json_instances, '_get_schema', mocked_get_schema)
+
+    def MockedRefResolver(base_uri, referrer, handlers):
+        """....<function replaces a class...>"""
+        assert base_uri == referrer['$id']
+        assert referrer == {'$id': 'dummy_uri'}
+        assert handlers == {'https': mocked_get_schema}
+        return 'dummy_resolver'
+
+    monkeypatch.setattr(json_instances, 'RefResolver', MockedRefResolver)
+
+    def MockedDraft7Validator(schema, resolver):
+        """....<same as above>"""
+        assert schema == {'$id': 'dummy_uri'}
+        assert resolver == 'dummy_resolver'
+        return 'dummy_validator'
+
+    monkeypatch.setattr(json_instances, 'Draft7Validator',
+                        MockedDraft7Validator)
+
+    assert json_instances.validator_for(_in) == 'dummy_validator'
+
+def test_parse_instance(monkeypatch):
+    """...."""
+    def mocked_strip_json_comments(text):
+        """...."""
+        assert text == 'dummy_commented_json'
+        return '{"dummy": 1}'
+
+    monkeypatch.setattr(json_instances, 'strip_json_comments',
+                        mocked_strip_json_comments)
+
+    assert json_instances.parse_instance('dummy_commented_json') == {'dummy': 1}
+
+
+def test_read_instance(monkeypatch, tmpdir):
+    """...."""
+    def mocked_parse_instance(text):
+        """...."""
+        assert text == 'dummy_JSON_text'
+        return {'dummy': 1}
+
+    monkeypatch.setattr(json_instances, 'parse_instance', mocked_parse_instance)
+
+    somepath = tmpdir / 'somefile'
+    somepath.write_text('dummy_JSON_text')
+
+    for instance_or_path in (somepath, str(somepath), {'dummy': 1}):
+        assert json_instances.read_instance(instance_or_path) == {'dummy': 1}
+
+def test_read_instance_bad(monkeypatch, tmpdir):
+    """...."""
+    monkeypatch.setattr(json_instances, 'parse_instance', lambda: 3 / 0)
+
+    somepath = tmpdir / 'somefile'
+    somepath.write_text('dummy_JSON_text')
+
+    error_regex = f'^text_in_{re.escape(str(somepath))}_not_valid_json$'
+    with pytest.raises(HaketiloException, match=error_regex):
+        json_instances.read_instance(somepath)
+
+@pytest.mark.parametrize('instance, ver_str', [
+    ({'$schema': 'a_b_c-1.0.1.0.schema.json'},   '1.0.1.0'),
+    ({'$schema': '9-9-9-10.5.600.schema.json'},  '10.5.600'),
+    ({'$schema': 'https://ab.cd-2.schema.json'}, '2')
+])
+def test_get_schema_version(instance, ver_str, monkeypatch):
+    """...."""
+    def mocked_parse_version(_ver_str):
+        """...."""
+        assert _ver_str == ver_str
+        return 'dummy_version'
+
+    monkeypatch.setattr(json_instances, 'parse_version', mocked_parse_version)
+
+    assert json_instances.get_schema_version(instance) == 'dummy_version'
+
+@pytest.mark.parametrize('instance', [
+    {'$schema': 'https://ab.cd-0.schema.json'},
+    {'$schema': 'https://ab.cd-02.schema.json'},
+    {'$schema': 'https://ab.cd-2.00.schema.json'},
+    {'$schema': 'https://ab.cd-2.01.schema.json'},
+    {'$schema': 'https://ab.cd-2.schema.json5'},
+    {'$schema': 'https://ab.cd-2.schema@json'},
+    {'$schema': 'https://ab.cd_2.schema.json'},
+    {'$schema': '2.schema.json'},
+    {'$schema': 'https://ab.cd-.schema.json'},
+    {'$schema': b'https://ab.cd-2.schema.json'},
+    {},
+    'not dict'
+])
+def test_get_schema_version_bad(instance):
+    """...."""
+    error_regex = '^no_schema_number_in_instance$'
+    with pytest.raises(HaketiloException, match=error_regex):
+        json_instances.get_schema_version(instance)
+
+def test_get_schema_major_number(monkeypatch):
+    """...."""
+    def mocked_get_schema_version(instance):
+        """...."""
+        assert instance == 'dummy_instance'
+        return (3, 4, 6)
+
+    monkeypatch.setattr(json_instances, 'get_schema_version',
+                        mocked_get_schema_version)
+
+    assert json_instances.get_schema_major_number('dummy_instance') == 3
+
+def test_validate_instance(monkeypatch):
+    """...."""
+    def mocked_get_schema_major_number(instance):
+        """...."""
+        assert instance == 'dummy_instance'
+        return 4
+
+    monkeypatch.setattr(json_instances, 'get_schema_major_number',
+                        mocked_get_schema_major_number)
+
+    class mocked_validator_for:
+        """....<class instead of function>"""
+        def __init__(self, schema_name):
+            """...."""
+            assert schema_name == 'https://ab.cd/something-4.schema.json'
+
+        def validate(self, instance):
+            """...."""
+            assert instance == 'dummy_instance'
+
+    monkeypatch.setattr(json_instances, 'validator_for', mocked_validator_for)
+
+    schema_name_fmt = 'https://ab.cd/something-{}.schema.json'
+    assert json_instances.validate_instance(
+        'dummy_instance',
+        schema_name_fmt
+    ) == 4
diff --git a/tests/test_local_apt.py b/tests/test_local_apt.py
new file mode 100644
index 0000000..9122408
--- /dev/null
+++ b/tests/test_local_apt.py
@@ -0,0 +1,754 @@
+# SPDX-License-Identifier: CC0-1.0
+
+# Copyright (C) 2022 Wojtek Kosior <koszko@koszko.org>
+#
+# Available under the terms of Creative Commons Zero v1.0 Universal.
+
+import pytest
+import tempfile
+import re
+import json
+from pathlib import Path, PurePosixPath
+from zipfile import ZipFile
+from tempfile import TemporaryDirectory
+
+from hydrilla.builder import local_apt
+from hydrilla.builder.common_errors import *
+
+here = Path(__file__).resolve().parent
+
+from .helpers import *
+
+@pytest.fixture
+def mock_cache_dir(monkeypatch):
+    """Make local_apt.py cache files to a temporary directory."""
+    with tempfile.TemporaryDirectory() as td:
+        td_path = Path(td)
+        monkeypatch.setattr(local_apt, 'default_apt_cache_dir', td_path)
+        yield td_path
+
+@pytest.fixture
+def mock_gnupg_import(monkeypatch, mock_cache_dir):
+    """Mock gnupg library when imported dynamically."""
+
+    gnupg_mock_dir = mock_cache_dir / 'gnupg_mock'
+    gnupg_mock_dir.mkdir()
+    (gnupg_mock_dir / 'gnupg.py').write_text('GPG = None\n')
+
+    monkeypatch.syspath_prepend(str(gnupg_mock_dir))
+
+    import gnupg
+
+    keyring_path = mock_cache_dir / 'master_keyring.gpg'
+
+    class MockedImportResult:
+        """gnupg.ImportResult replacement"""
+        def __init__(self):
+            """Initialize MockedImportResult object."""
+            self.imported = 1
+
+    class MockedGPG:
+        """GPG replacement that does not really invoke GPG."""
+        def __init__(self, keyring):
+            """Verify the keyring path and initialize MockedGPG."""
+            assert keyring == str(keyring_path)
+
+            self.known_keys = {*keyring_path.read_text().split('\n')} \
+                if keyring_path.exists() else set()
+
+        def recv_keys(self, keyserver, key):
+            """Mock key receiving - record requested key as received."""
+            assert keyserver == local_apt.default_keyserver
+            assert key not in self.known_keys
+
+            self.known_keys.add(key)
+            keyring_path.write_text('\n'.join(self.known_keys))
+
+            return MockedImportResult()
+
+        def list_keys(self, keys=None):
+            """Mock key listing - return a list with dummy items."""
+            if keys is None:
+                return ['dummy'] * len(self.known_keys)
+            else:
+                return ['dummy' for k in keys if k in self.known_keys]
+
+        def export_keys(self, keys, **kwargs):
+            """
+            Mock key export - check that the call has the expected arguments and
+            return a dummy bytes array.
+            """
+            assert kwargs['armor']   == False
+            assert kwargs['minimal'] == True
+            assert {*keys} == self.known_keys
+
+            return b'<dummy keys export>'
+
+    monkeypatch.setattr(gnupg, 'GPG', MockedGPG)
+
+def process_run_args(command, kwargs, expected_command):
+    """
+    Perform assertions common to all mocked subprocess.run() invocations and
+    extract variable parts of the command line (if any).
+    """
+    assert kwargs['env'] == {'LANG': 'en_US'}
+    assert kwargs['capture_output'] == True
+
+    return process_command(command, expected_command)
+
+def run_apt_get_update(command, returncode=0, **kwargs):
+    """
+    Instead of running an 'apt-get update' command just touch some file in apt
+    root to indicate that the call was made.
+    """
+    expected = ['apt-get', '-c', '<conf_path>', 'update']
+    conf_path = Path(process_run_args(command, kwargs, expected)['conf_path'])
+
+    (conf_path.parent / 'update_called').touch()
+
+    return MockedCompletedProcess(command, returncode,
+                                  text_output=kwargs.get('text'))
+
+"""
+Output of 'apt-get install --yes --just-print libjs-mathjax' on some APT-based
+system.
+"""
+sample_install_stdout = '''\
+NOTE: This is only a simulation!
+      apt-get needs root privileges for real execution.
+      Keep also in mind that locking is deactivated,
+      so don't depend on the relevance to the real current situation!
+Reading package lists...
+Building dependency tree...
+Reading state information...
+The following additional packages will be installed:
+  fonts-mathjax
+Suggested packages:
+  fonts-mathjax-extras fonts-stix libjs-mathjax-doc
+The following NEW packages will be installed:
+  fonts-mathjax libjs-mathjax
+0 upgraded, 2 newly installed, 0 to remove and 0 not upgraded.
+Inst fonts-mathjax (0:2.7.9+dfsg-1 Devuan:4.0/stable, Devuan:1.0.0/unstable [all])
+Inst libjs-mathjax (0:2.7.9+dfsg-1 Devuan:4.0/stable, Devuan:1.0.0/unstable [all])
+Conf fonts-mathjax (0:2.7.9+dfsg-1 Devuan:4.0/stable, Devuan:1.0.0/unstable [all])
+Conf libjs-mathjax (0:2.7.9+dfsg-1 Devuan:4.0/stable, Devuan:1.0.0/unstable [all])
+'''
+
+def run_apt_get_install(command, returncode=0, **kwargs):
+    """
+    Instead of running an 'apt-get install' command just print a possible
+    output of one.
+    """
+    expected = ['apt-get', '-c', '<conf_path>', 'install',
+                '--yes', '--just-print', 'libjs-mathjax']
+
+    conf_path = Path(process_run_args(command, kwargs, expected)['conf_path'])
+
+    return MockedCompletedProcess(command, returncode,
+                                  stdout=sample_install_stdout,
+                                  text_output=kwargs.get('text'))
+
+def run_apt_get_download(command, returncode=0, **kwargs):
+    """
+    Instead of running an 'apt-get download' command just write some dummy
+    .deb to the appropriate directory.
+    """
+    expected = ['apt-get', '-c', '<conf_path>', 'download']
+    if 'libjs-mathjax' in command:
+        expected.append('libjs-mathjax')
+    else:
+        expected.append('fonts-mathjax=0:2.7.9+dfsg-1')
+        expected.append('libjs-mathjax=0:2.7.9+dfsg-1')
+
+    conf_path = Path(process_run_args(command, kwargs, expected)['conf_path'])
+
+    destination = Path(kwargs.get('cwd') or Path.cwd())
+
+    package_name_regex = re.compile(r'^[^=]+-mathjax')
+
+    for word in expected:
+        match = package_name_regex.match(word)
+        if match:
+            filename = f'{match.group(0)}_0%3a2.7.9+dfsg-1_all.deb'
+            deb_path = destination / filename
+            deb_path.write_text(f'dummy {deb_path.name}')
+
+    return MockedCompletedProcess(command, returncode,
+                                  text_output=kwargs.get('text'))
+
+def run_apt_get_source(command, returncode=0, **kwargs):
+    """
+    Instead of running an 'apt-get source' command just write some dummy
+    "tarballs" to the appropriate directory.
+    """
+    expected = ['apt-get', '-c', '<conf_path>', 'source',
+                '--download-only', 'libjs-mathjax=0:2.7.9+dfsg-1']
+    if 'fonts-mathjax=0:2.7.9+dfsg-1' in command:
+        if command[-1] == 'fonts-mathjax=0:2.7.9+dfsg-1':
+            expected.append('fonts-mathjax=0:2.7.9+dfsg-1')
+        else:
+            expected.insert(-1, 'fonts-mathjax=0:2.7.9+dfsg-1')
+
+    destination = Path(kwargs.get('cwd') or Path.cwd())
+    for filename in [
+        'mathjax_2.7.9+dfsg-1.debian.tar.xz',
+        'mathjax_2.7.9+dfsg-1.dsc',
+        'mathjax_2.7.9+dfsg.orig.tar.xz'
+    ]:
+        (destination / filename).write_text(f'dummy {filename}')
+
+    return MockedCompletedProcess(command, returncode,
+                                  text_output=kwargs.get('text'))
+
+def make_run_apt_get(**returncodes):
+    """
+    Produce a function that chooses and runs the appropriate one of
+    subprocess_run_apt_get_*() mock functions.
+    """
+    def mock_run(command, **kwargs):
+        """
+        Chooses and runs the appropriate one of subprocess_run_apt_get_*() mock
+        functions.
+        """
+        for subcommand, run in [
+            ('update',   run_apt_get_update),
+            ('install',  run_apt_get_install),
+            ('download', run_apt_get_download),
+            ('source',   run_apt_get_source)
+        ]:
+            if subcommand in command:
+                returncode = returncodes.get(f'{subcommand}_code', 0)
+                return run(command, returncode, **kwargs)
+
+        raise Exception('Unknown command: {}'.format(' '.join(command)))
+
+    return mock_run
+
+@pytest.mark.subprocess_run(local_apt, make_run_apt_get())
+@pytest.mark.usefixtures('mock_subprocess_run', 'mock_gnupg_import')
+def test_local_apt_contextmanager(mock_cache_dir):
+    """
+    Verify that the local_apt() function creates a proper apt environment and
+    that it also properly restores it from cache.
+    """
+    sources_list = local_apt.SourcesList(['deb-src sth', 'deb sth'])
+
+    with local_apt.local_apt(sources_list, local_apt.default_keys) as apt:
+        apt_root = Path(apt.apt_conf).parent.parent
+
+        assert (apt_root / 'etc' / 'trusted.gpg').read_bytes() == \
+            b'<dummy keys export>'
+
+        assert (apt_root / 'etc' / 'update_called').exists()
+
+        assert (apt_root / 'etc' / 'apt.sources.list').read_text() == \
+            'deb-src sth\ndeb sth'
+
+        conf_lines = (apt_root / 'etc' / 'apt.conf').read_text().split('\n')
+
+        # check mocked keyring
+        assert {*local_apt.default_keys} == \
+            {*(mock_cache_dir / 'master_keyring.gpg').read_text().split('\n')}
+
+    assert not apt_root.exists()
+
+    expected_conf = {
+        'Architecture':           'amd64',
+        'Dir':                    str(apt_root),
+        'Dir::State':             f'{apt_root}/var/lib/apt',
+        'Dir::State::status':     f'{apt_root}/var/lib/dpkg/status',
+        'Dir::Etc::SourceList':   f'{apt_root}/etc/apt.sources.list',
+        'Dir::Etc::SourceParts':  '',
+        'Dir::Cache':             f'{apt_root}/var/cache/apt',
+        'pkgCacheGen::Essential': 'none',
+        'Dir::Etc::Trusted':      f'{apt_root}/etc/trusted.gpg',
+    }
+
+    conf_regex = re.compile(r'^(?P<key>\S+)\s"(?P<val>\S*)";$')
+    assert dict([(m.group('key'), m.group('val'))
+                 for l in conf_lines if l for m in [conf_regex.match(l)]]) == \
+        expected_conf
+
+    with ZipFile(mock_cache_dir / f'apt_{sources_list.identity()}.zip') as zf:
+        # reuse the same APT, its cached zip file should exist now
+        with local_apt.local_apt(sources_list, local_apt.default_keys) as apt:
+            apt_root = Path(apt.apt_conf).parent.parent
+
+            expected_members = {*apt_root.rglob('*')}
+            expected_members.remove(apt_root / 'etc' / 'apt.conf')
+            expected_members.remove(apt_root / 'etc' / 'trusted.gpg')
+
+            names = zf.namelist()
+            assert len(names) == len(expected_members)
+
+            for name in names:
+                path = apt_root / name
+                assert path in expected_members
+                assert zf.read(name) == \
+                    (b'' if path.is_dir() else path.read_bytes())
+
+    assert not apt_root.exists()
+
+@pytest.mark.subprocess_run(local_apt, run_missing_executable)
+@pytest.mark.usefixtures('mock_subprocess_run', 'mock_gnupg_import')
+def test_local_apt_missing(mock_cache_dir):
+    """
+    Verify that the local_apt() function raises a proper error when 'apt-get'
+    command is missing.
+    """
+    sources_list = local_apt.SourcesList(['deb-src sth', 'deb sth'])
+
+    with pytest.raises(local_apt.AptError,
+                       match='^couldnt_execute_apt-get_is_it_installed$'):
+        with local_apt.local_apt(sources_list, local_apt.default_keys) as apt:
+            pass
+
+@pytest.mark.subprocess_run(local_apt, make_run_apt_get(update_code=1))
+@pytest.mark.usefixtures('mock_subprocess_run', 'mock_gnupg_import')
+def test_local_apt_update_fail(mock_cache_dir):
+    """
+    Verify that the local_apt() function raises a proper error when
+    'apt-get update' command returns non-0.
+    """
+    sources_list = local_apt.SourcesList(['deb-src sth', 'deb sth'])
+
+    error_regex = """^\
+command_apt-get -c \\S+ update_failed
+
+STDOUT_OUTPUT_heading
+
+some output
+
+STDERR_OUTPUT_heading
+
+some error output\
+$\
+"""
+
+    with pytest.raises(local_apt.AptError, match=error_regex):
+        with local_apt.local_apt(sources_list, local_apt.default_keys) as apt:
+            pass
+
+@pytest.mark.subprocess_run(local_apt, make_run_apt_get())
+@pytest.mark.usefixtures('mock_subprocess_run', 'mock_gnupg_import')
+def test_local_apt_download(mock_cache_dir):
+    """
+    Verify that download_apt_packages() function properly performs the download
+    of .debs and sources.
+    """
+    sources_list = local_apt.SourcesList(['deb-src sth', 'deb sth'])
+    destination = mock_cache_dir / 'destination'
+    destination.mkdir()
+
+    local_apt.download_apt_packages(sources_list, local_apt.default_keys,
+                                    ['libjs-mathjax'], destination, False)
+
+    libjs_mathjax_path = destination / 'libjs-mathjax_0%3a2.7.9+dfsg-1_all.deb'
+    fonts_mathjax_path = destination / 'fonts-mathjax_0%3a2.7.9+dfsg-1_all.deb'
+
+    source_paths = [
+        destination / 'mathjax_2.7.9+dfsg-1.debian.tar.xz',
+        destination / 'mathjax_2.7.9+dfsg-1.dsc',
+        destination / 'mathjax_2.7.9+dfsg.orig.tar.xz'
+    ]
+
+    assert {*destination.iterdir()} == {libjs_mathjax_path, *source_paths}
+
+    local_apt.download_apt_packages(sources_list, local_apt.default_keys,
+                                    ['libjs-mathjax'], destination,
+                                    with_deps=True)
+
+    assert {*destination.iterdir()} == \
+        {libjs_mathjax_path, fonts_mathjax_path, *source_paths}
+
+@pytest.mark.subprocess_run(local_apt, make_run_apt_get(install_code=1))
+@pytest.mark.usefixtures('mock_subprocess_run', 'mock_gnupg_import')
+def test_local_apt_install_fail(mock_cache_dir):
+    """
+    Verify that the download_apt_packages() function raises a proper error when
+    'apt-get install' command returns non-0.
+    """
+    sources_list = local_apt.SourcesList(['deb-src sth', 'deb sth'])
+    destination = mock_cache_dir / 'destination'
+    destination.mkdir()
+
+    error_regex = f"""^\
+command_apt-get -c \\S+ install --yes --just-print libjs-mathjax_failed
+
+STDOUT_OUTPUT_heading
+
+{re.escape(sample_install_stdout)}
+
+STDERR_OUTPUT_heading
+
+some error output\
+$\
+"""
+
+    with pytest.raises(local_apt.AptError, match=error_regex):
+        local_apt.download_apt_packages(sources_list, local_apt.default_keys,
+                                        ['libjs-mathjax'], destination,
+                                        with_deps=True)
+
+    assert [*destination.iterdir()] == []
+
+@pytest.mark.subprocess_run(local_apt, make_run_apt_get(download_code=1))
+@pytest.mark.usefixtures('mock_subprocess_run', 'mock_gnupg_import')
+def test_local_apt_download_fail(mock_cache_dir):
+    """
+    Verify that the download_apt_packages() function raises a proper error when
+    'apt-get download' command returns non-0.
+    """
+    sources_list = local_apt.SourcesList(['deb-src sth', 'deb sth'])
+    destination = mock_cache_dir / 'destination'
+    destination.mkdir()
+
+    error_regex = """^\
+command_apt-get -c \\S+ download libjs-mathjax_failed
+
+STDOUT_OUTPUT_heading
+
+some output
+
+STDERR_OUTPUT_heading
+
+some error output\
+$\
+"""
+
+    with pytest.raises(local_apt.AptError, match=error_regex):
+        local_apt.download_apt_packages(sources_list, local_apt.default_keys,
+                                        ['libjs-mathjax'], destination, False)
+
+    assert [*destination.iterdir()] == []
+
+@pytest.fixture
+def mock_bad_deb_file(monkeypatch, mock_subprocess_run):
+    """
+    Make mocked 'apt-get download' command produce an incorrectly-named file.
+    """
+    old_run = local_apt.subprocess.run
+
+    def twice_mocked_run(command, **kwargs):
+        """
+        Create an evil file if needed; then act just like the run() function
+        that got replaced by this one.
+        """
+        if 'download' in command:
+            destination = Path(kwargs.get('cwd') or Path.cwd())
+            (destination / 'arbitrary-name').write_text('anything')
+
+        return old_run(command, **kwargs)
+
+    monkeypatch.setattr(local_apt.subprocess, 'run', twice_mocked_run)
+
+@pytest.mark.subprocess_run(local_apt, make_run_apt_get())
+@pytest.mark.usefixtures('mock_subprocess_run', 'mock_gnupg_import',
+                         'mock_bad_deb_file')
+def test_local_apt_download_bad_filename(mock_cache_dir):
+    """
+    Verify that the download_apt_packages() function raises a proper error when
+    'apt-get download' command produces an incorrectly-named file.
+    """
+    sources_list = local_apt.SourcesList([], 'nabia')
+    destination = mock_cache_dir / 'destination'
+    destination.mkdir()
+
+    error_regex = """^\
+apt_download_gave_bad_filename_arbitrary-name
+
+STDOUT_OUTPUT_heading
+
+some output
+
+STDERR_OUTPUT_heading
+
+some error output\
+$\
+"""
+
+    with pytest.raises(local_apt.AptError, match=error_regex):
+        local_apt.download_apt_packages(sources_list, local_apt.default_keys,
+                                        ['libjs-mathjax'], destination, False)
+
+    assert [*destination.iterdir()] == []
+
+@pytest.mark.subprocess_run(local_apt, make_run_apt_get(source_code=1))
+@pytest.mark.usefixtures('mock_subprocess_run', 'mock_gnupg_import')
+def test_local_apt_source_fail(mock_cache_dir):
+    """
+    Verify that the download_apt_packages() function raises a proper error when
+    'apt-get source' command returns non-0.
+    """
+    sources_list = local_apt.SourcesList(['deb-src sth', 'deb sth'])
+    destination = mock_cache_dir / 'destination'
+    destination.mkdir()
+
+    error_regex = """^\
+command_apt-get -c \\S* source --download-only \\S+_failed
+
+STDOUT_OUTPUT_heading
+
+some output
+
+STDERR_OUTPUT_heading
+
+some error output\
+$\
+"""
+
+    with pytest.raises(local_apt.AptError, match=error_regex):
+        local_apt.download_apt_packages(sources_list, local_apt.default_keys,
+                                        ['libjs-mathjax'], destination, False)
+
+    assert [*destination.iterdir()] == []
+
+def test_sources_list():
+    """Verify that the SourcesList class works properly."""
+    list = local_apt.SourcesList([], 'nabia')
+    assert list.identity() == 'nabia'
+
+    with pytest.raises(local_apt.DistroError, match='^distro_nabiał_unknown$'):
+        local_apt.SourcesList([], 'nabiał')
+
+    list = local_apt.SourcesList(['deb sth', 'deb-src sth'], 'nabia')
+    assert list.identity() == \
+        'ef28d408b96046eae45c8ab3094ce69b2ac0c02a887e796b1d3d1a4f06fb49f1'
+
+def run_dpkg_deb(command, returncode=0, **kwargs):
+    """
+    Insted of running an 'dpkg-deb -x' command just create some dummy file
+    in the destination directory.
+    """
+    expected = ['dpkg-deb', '-x', '<deb_path>', '<dst_path>']
+
+    variables = process_run_args(command, kwargs, expected)
+    deb_path = Path(variables['deb_path'])
+    dst_path = Path(variables['dst_path'])
+
+    package_name = re.match('^([^_]+)_.*', deb_path.name).group(1)
+    for path in [
+            dst_path / 'etc' / f'dummy_{package_name}_config',
+            dst_path / 'usr/share/doc' / package_name / 'copyright'
+    ]:
+        path.parent.mkdir(parents=True, exist_ok=True)
+        path.write_text(f'dummy {path.name}')
+
+    return MockedCompletedProcess(command, returncode,
+                                  text_output=kwargs.get('text'))
+
+def download_apt_packages(list, keys, packages, destination_dir,
+                          with_deps=False):
+    """
+    Replacement for download_apt_packages() function in local_apt.py, for
+    unit-testing the piggybacked_system() function.
+    """
+    for path in [
+            destination_dir / 'some-bin-package_1.1-2_all.deb',
+            destination_dir / 'another-package_1.1-2_all.deb',
+            destination_dir / 'some-source-package_1.1.orig.tar.gz',
+            destination_dir / 'some-source-package_1.1-1.dsc'
+    ]:
+        path.write_text(f'dummy {path.name}')
+
+    with open(destination_dir / 'test_data.json', 'w') as out:
+        json.dump({
+            'list_identity': list.identity(),
+            'keys': keys,
+            'packages': packages,
+            'with_deps': with_deps
+        }, out)
+
+@pytest.fixture
+def mock_download_packages(monkeypatch):
+    """Mock the download_apt_packages() function in local_apt.py."""
+    monkeypatch.setattr(local_apt, 'download_apt_packages',
+                        download_apt_packages)
+
+@pytest.mark.subprocess_run(local_apt, run_dpkg_deb)
+@pytest.mark.parametrize('params', [
+    {
+        'with_deps': False,
+        'base_depends': True,
+        'identity': 'nabia',
+        'props': {'distribution': 'nabia', 'dependencies': False},
+        'all_keys': local_apt.default_keys,
+        'prepared_directory': False
+    },
+    {
+        'with_deps': True,
+        'base_depends': False,
+        'identity': '38db0b4fa2f6610cd1398b66a2c05d9abb1285f9a055a96eb96dee0f6b72aca8',
+        'props': {
+            'sources_list': [f'deb{suf} http://example.com/ stable main'
+                             for suf in ('', '-src')],
+            'trusted_keys': ['AB' * 20],
+            'dependencies': True,
+            'depend_on_base_packages': False
+        },
+        'all_keys': [*local_apt.default_keys, 'AB' * 20],
+        'prepared_directory': True
+    }
+])
+@pytest.mark.usefixtures('mock_download_packages', 'mock_subprocess_run')
+def test_piggybacked_system_download(params, tmpdir):
+    """
+    Verify that the piggybacked_system() function properly downloads and unpacks
+    APT packages.
+    """
+    foreign_packages_dir = tmpdir if params['prepared_directory'] else None
+
+    with local_apt.piggybacked_system({
+            'system': 'apt',
+            **params['props'],
+            'packages': ['some-bin-package', 'another-package=1.1-2']
+    }, foreign_packages_dir) as piggybacked:
+        expected_depends = [{'identifier': 'apt-common-licenses'}] \
+            if params['base_depends'] else []
+        assert piggybacked.resource_must_depend == expected_depends
+
+        archive_files = dict(piggybacked.archive_files())
+
+        archive_names = [
+            'some-bin-package_1.1-2_all.deb',
+            'another-package_1.1-2_all.deb',
+            'some-source-package_1.1.orig.tar.gz',
+            'some-source-package_1.1-1.dsc',
+            'test_data.json'
+        ]
+        assert {*archive_files.keys()} == \
+            {PurePosixPath('apt') / n for n in archive_names}
+
+        for path in archive_files.values():
+            if path.name == 'test_data.json':
+                assert json.loads(path.read_text()) == {
+                    'list_identity': params['identity'],
+                    'keys': params['all_keys'],
+                    'packages': ['some-bin-package', 'another-package=1.1-2'],
+                    'with_deps': params['with_deps']
+                }
+            else:
+                assert path.read_text() == f'dummy {path.name}'
+
+            if foreign_packages_dir is not None:
+                assert path.parent == foreign_packages_dir / 'apt'
+
+        license_files = {*piggybacked.package_license_files}
+
+        assert license_files == {
+            PurePosixPath('.apt-root/usr/share/doc/another-package/copyright'),
+            PurePosixPath('.apt-root/usr/share/doc/some-bin-package/copyright')
+        }
+
+        assert ['dummy copyright'] * 2 == \
+            [piggybacked.resolve_file(p).read_text() for p in license_files]
+
+        for name in ['some-bin-package', 'another-package']:
+            path = PurePosixPath(f'.apt-root/etc/dummy_{name}_config')
+            assert piggybacked.resolve_file(path).read_text() == \
+                f'dummy {path.name}'
+
+        assert piggybacked.resolve_file(PurePosixPath('a/b/c')) == None
+        assert piggybacked.resolve_file(PurePosixPath('')) == None
+
+        output_text = 'loading_.apt-root/a/../../../b_outside_piggybacked_dir'
+        with pytest.raises(FileReferenceError,
+                           match=f'^{re.escape(output_text)}$'):
+            piggybacked.resolve_file(PurePosixPath('.apt-root/a/../../../b'))
+
+        root = piggybacked.resolve_file(PurePosixPath('.apt-root/dummy')).parent
+        assert root.is_dir()
+
+    assert not root.exists()
+
+    if foreign_packages_dir:
+        assert [*tmpdir.iterdir()] == [tmpdir / 'apt']
+
+@pytest.mark.subprocess_run(local_apt, run_dpkg_deb)
+@pytest.mark.usefixtures('mock_subprocess_run')
+def test_piggybacked_system_no_download():
+    """
+    Verify that the piggybacked_system() function is able to use pre-downloaded
+    APT packages.
+    """
+    archive_names = {
+        f'{package}{rest}'
+        for package in ('some-lib_1:2.3', 'other-lib_4.45.2')
+        for rest in ('-1_all.deb', '.orig.tar.gz', '-1.debian.tar.xz', '-1.dsc')
+    }
+
+    with TemporaryDirectory() as td:
+        td = Path(td)
+        (td / 'apt').mkdir()
+        for name in archive_names:
+            (td / 'apt' / name).write_text(f'dummy {name}')
+
+        with local_apt.piggybacked_system({
+                'system': 'apt',
+                'distribution': 'nabia',
+                'dependencies': True,
+                'packages': ['whatever', 'whatever2']
+        }, td) as piggybacked:
+            archive_files = dict(piggybacked.archive_files())
+
+            assert {*archive_files.keys()} == \
+                {PurePosixPath('apt') / name for name in archive_names}
+
+            for path in archive_files.values():
+                assert path.read_text() == f'dummy {path.name}'
+
+            assert {*piggybacked.package_license_files} == {
+                PurePosixPath('.apt-root/usr/share/doc/some-lib/copyright'),
+                PurePosixPath('.apt-root/usr/share/doc/other-lib/copyright')
+            }
+
+            for name in ['some-lib', 'other-lib']:
+                path = PurePosixPath(f'.apt-root/etc/dummy_{name}_config')
+                assert piggybacked.resolve_file(path).read_text() == \
+                    f'dummy {path.name}'
+
+@pytest.mark.subprocess_run(local_apt, run_missing_executable)
+@pytest.mark.usefixtures('mock_download_packages', 'mock_subprocess_run')
+def test_piggybacked_system_missing():
+    """
+    Verify that the piggybacked_system() function raises a proper error when
+    'dpkg-deb' is missing.
+    """
+    with pytest.raises(local_apt.AptError,
+                       match='^couldnt_execute_dpkg-deb_is_it_installed$'):
+        with local_apt.piggybacked_system({
+                'system': 'apt',
+                'distribution': 'nabia',
+                'packages': ['some-package'],
+                'dependencies': False
+        }, None) as piggybacked:
+            pass
+
+@pytest.mark.subprocess_run(local_apt, lambda c, **kw: run_dpkg_deb(c, 1, **kw))
+@pytest.mark.usefixtures('mock_download_packages', 'mock_subprocess_run')
+def test_piggybacked_system_fail():
+    """
+    Verify that the piggybacked_system() function raises a proper error when
+    'dpkg-deb -x' command returns non-0.
+    """
+    error_regex = """^\
+command_dpkg-deb -x \\S+\\.deb \\S+_failed
+
+STDOUT_OUTPUT_heading
+
+some output
+
+STDERR_OUTPUT_heading
+
+some error output\
+$\
+"""
+
+    with pytest.raises(local_apt.AptError, match=error_regex):
+        with local_apt.piggybacked_system({
+                'system': 'apt',
+                'distribution': 'nabia',
+                'packages': ['some-package'],
+                'dependencies': False
+        }, None) as piggybacked:
+            pass
diff --git a/tests/test_pattern_tree.py b/tests/test_pattern_tree.py
new file mode 100644
index 0000000..4238d66
--- /dev/null
+++ b/tests/test_pattern_tree.py
@@ -0,0 +1,454 @@
+# SPDX-License-Identifier: CC0-1.0
+
+# Copyright (C) 2022 Wojtek Kosior <koszko@koszko.org>
+#
+# Available under the terms of Creative Commons Zero v1.0 Universal.
+
+import pytest
+import re
+import dataclasses as dc
+
+from immutables import Map
+
+from hydrilla import pattern_tree
+
+from .url_patterns_common import *
+
+@pytest.mark.parametrize('_in, out', [
+    (Map(),                                                  True),
+    ({'children': Map(non_empty='non_emtpy')},               False),
+    ({'literal_match': 'non-None'},                          False),
+    ({'children': Map(non_empty='non_emtpy')},               False),
+    ({'literal_match': 'non-None', 'children': 'non-empty'}, False)
+])
+def test_pattern_tree_node_is_empty(_in, out):
+    """...."""
+    assert pattern_tree.PatternTreeNode(**_in).is_empty() == out
+
+def test_pattern_tree_node_update_literal_match():
+    """...."""
+    node1 = pattern_tree.PatternTreeNode()
+    node2 = node1.update_literal_match('dummy match item')
+
+    assert node1.literal_match is None
+    assert node2.literal_match == 'dummy match item'
+
+def test_pattern_tree_node_get_child():
+    """...."""
+    node = pattern_tree.PatternTreeNode(children=Map(dummy_key='dummy_val'))
+
+    assert node.get_child('dummy_key') == 'dummy_val'
+    assert node.get_child('other_key') is None
+
+def test_pattern_tree_node_remove_child():
+    """...."""
+    node1 = pattern_tree.PatternTreeNode(children=Map(dummy_key='dummy_val'))
+    node2 = node1.remove_child('dummy_key')
+
+    assert node1.children == Map(dummy_key='dummy_val')
+    assert node2.children == Map()
+
+def test_pattern_tree_node_set_child():
+    """...."""
+    node1 = pattern_tree.PatternTreeNode(children=Map(dummy_key='dummy_val'))
+    node2 = node1.set_child('other_key', 'other_val')
+
+    assert node1.children == Map(dummy_key='dummy_val')
+    assert node2.children == Map(dummy_key='dummy_val', other_key='other_val')
+
+@pytest.mark.parametrize('root_empty', [True, False])
+def test_pattern_tree_branch_is_empty(root_empty):
+    """...."""
+    class DummyEmptyRoot:
+        """...."""
+        is_empty = lambda: root_empty
+
+    branch = pattern_tree.PatternTreeBranch(root_node=DummyEmptyRoot)
+    assert branch.is_empty() == root_empty
+
+# def test_pattern_tree_branch_copy():
+#     """...."""
+#     class DummyRoot:
+#         """...."""
+#         pass
+
+#     branch1 = pattern_tree.PatternTreeBranch(root_node=DummyRoot)
+#     branch2 = branch1.copy()
+
+#     assert branch1 is not branch2
+#     for val_b1, val_b2 in zip(dc.astuple(branch1), dc.astuple(branch2)):
+#         assert val_b1 is val_b2
+
+@pytest.fixture
+def empty_branch():
+    """...."""
+    return pattern_tree.PatternTreeBranch(
+        root_node = pattern_tree.PatternTreeNode()
+    )
+
+@pytest.fixture
+def branch_with_a_b():
+    """...."""
+    return pattern_tree.PatternTreeBranch(
+        root_node = pattern_tree.PatternTreeNode(
+            children = Map(
+                a = pattern_tree.PatternTreeNode(
+                    children = Map(
+                        b = pattern_tree.PatternTreeNode(
+                            literal_match = frozenset({'myitem'})
+                        )
+                    )
+                )
+            )
+        )
+    )
+
+def test_pattern_tree_branch_update_add_first(empty_branch, branch_with_a_b):
+    """...."""
+    updated_branch = empty_branch.update(
+        ['a', 'b'],
+        lambda s: frozenset({*(s or []), 'myitem'})
+    )
+
+    assert updated_branch                  == branch_with_a_b
+    assert empty_branch.root_node.children == Map()
+
+def test_pattern_tree_branch_update_add_second(branch_with_a_b):
+    """...."""
+    updated_branch = branch_with_a_b.update(
+        ['a', 'b'],
+        lambda s: frozenset({*(s or []), 'myotheritem'})
+    )
+
+    leaf_node = updated_branch.root_node.children['a'].children['b']
+    assert leaf_node.literal_match == frozenset({'myitem', 'myotheritem'})
+
+def test_pattern_tree_branch_update_add_different_path(branch_with_a_b):
+    """...."""
+    updated_branch = branch_with_a_b.update(
+        ['a', 'not_b'],
+        lambda s: frozenset({*(s or []), 'myotheritem'})
+    )
+
+    for segment, item in [('b', 'myitem'), ('not_b', 'myotheritem')]:
+        leaf_node = updated_branch.root_node.children['a'].children[segment]
+        assert leaf_node.literal_match == frozenset({item})
+
+# def test_pattern_tree_branch_update_is_value_copied(branch_with_a_b):
+#     """...."""
+#     updated_branch = branch_with_a_b.update(['a', 'b'], lambda s: s)
+
+#     leaf_node_orig = updated_branch.root_node.children['a'].children['b']
+#     leaf_node_new  = branch_with_a_b.root_node.children['a'].children['b']
+
+#     assert leaf_node_orig.literal_match == leaf_node_new.literal_match
+#     assert leaf_node_orig.literal_match is not leaf_node_new.literal_match
+
+def test_pattern_tree_branch_remove(branch_with_a_b, empty_branch):
+    """...."""
+    updated_branch = branch_with_a_b.update(['a', 'b'], lambda s: None)
+
+    assert updated_branch == empty_branch
+
+def test_pattern_tree_branch_search_empty(empty_branch):
+    """...."""
+    assert [*empty_branch.search(['a', 'b'])] == []
+
+@pytest.fixture
+def branch_with_wildcards():
+    """...."""
+    return pattern_tree.PatternTreeBranch(
+        root_node = pattern_tree.PatternTreeNode(
+            children = Map(
+                a = pattern_tree.PatternTreeNode(
+                    children = Map(
+                        b = pattern_tree.PatternTreeNode(
+                            children = Map({
+                                'c': pattern_tree.PatternTreeNode(
+                                    literal_match = 'dummy/c'
+                                ),
+                                '*': pattern_tree.PatternTreeNode(
+                                    literal_match = 'dummy/*'
+                                ),
+                                '**': pattern_tree.PatternTreeNode(
+                                    literal_match = 'dummy/**'
+                                ),
+                                '***': pattern_tree.PatternTreeNode(
+                                    literal_match = 'dummy/***'
+                                )
+                            })
+                        )
+                    )
+                )
+            )
+        )
+    )
+
+@pytest.mark.parametrize('_in, out', [
+    (['a'],                       []),
+    (['a', 'x', 'y', 'z'],        []),
+    (['a', 'b'],                  ['dummy/***']),
+    (['a', 'b', 'c'],             ['dummy/c', 'dummy/*', 'dummy/***']),
+    (['a', 'b', 'u'],             ['dummy/*', 'dummy/***']),
+    (['a', 'b', '*'],             ['dummy/*', 'dummy/***']),
+    (['a', 'b', '**'],            ['dummy/**', 'dummy/*', 'dummy/***']),
+    (['a', 'b', '***'],           ['dummy/***', 'dummy/*']),
+    (['a', 'b', 'u', 'l'],        ['dummy/**', 'dummy/***']),
+    (['a', 'b', 'u', 'l', 'y'],   ['dummy/**', 'dummy/***'])
+])
+def test_pattern_tree_branch_search_wildcards(_in, out, branch_with_wildcards):
+    """...."""
+    assert [*branch_with_wildcards.search(_in)] == out
+
+def test_filter_by_trailing_slash(sample_url_parsed):
+    """...."""
+    sample_url_parsed2 = dc.replace(sample_url_parsed, has_trailing_slash=True)
+    item1 = pattern_tree.StoredTreeItem(sample_url_parsed,  'dummy_it1')
+    item2 = pattern_tree.StoredTreeItem(sample_url_parsed2, 'dummy_it2')
+
+    assert pattern_tree.filter_by_trailing_slash((item1, item2), False) == \
+        frozenset({item1})
+
+    assert pattern_tree.filter_by_trailing_slash((item1, item2), True) == \
+        frozenset({item2})
+
+@pytest.mark.parametrize('register_mode',  [True, False])
+@pytest.mark.parametrize('empty_at_start', [True, False])
+@pytest.mark.parametrize('empty_at_end',   [True, False])
+def test_pattern_tree_privatemethod_register(
+        register_mode,
+        empty_at_start,
+        empty_at_end,
+        monkeypatch,
+        sample_url_parsed
+):
+    """...."""
+    dummy_it       = pattern_tree.StoredTreeItem(sample_url_parsed, 'dummy_it')
+    other_dummy_it = pattern_tree.StoredTreeItem(
+        sample_url_parsed,
+        'other_dummy_it'
+    )
+
+    class MockedTreeBranch:
+        """...."""
+        def is_empty(self):
+            """...."""
+            return empty_at_end
+
+        def update(self, segments, item_updater):
+            """...."""
+            if segments == ('com', 'example'):
+                return self._update_as_domain_branch(item_updater)
+            else:
+                assert segments == ('aa', 'bb')
+                return self._update_as_path_branch(item_updater)
+
+        def _update_as_domain_branch(self, item_updater):
+            """...."""
+            for updater_input in (None, MockedTreeBranch()):
+                updated = item_updater(updater_input)
+                if empty_at_end:
+                    assert updated is None
+                else:
+                    assert type(updated) is MockedTreeBranch
+
+            return MockedTreeBranch()
+
+        def _update_as_path_branch(self, item_updater):
+            """...."""
+            set_with_1_item  = frozenset()
+            set_with_2_items = frozenset({dummy_it, other_dummy_it})
+            for updater_input in (None, set_with_1_item, set_with_2_items):
+                updated = item_updater(updater_input)
+                if register_mode:
+                    assert dummy_it in updated
+                elif updater_input is set_with_2_items:
+                    assert dummy_it not in updated
+                else:
+                    assert updated is None
+
+            return MockedTreeBranch()
+
+    monkeypatch.setattr(pattern_tree, 'PatternTreeBranch', MockedTreeBranch)
+
+    initial_root = Map() if empty_at_start else \
+        Map({('http', 80): MockedTreeBranch()})
+
+    tree = pattern_tree.PatternTree(_by_scheme_and_port=initial_root)
+
+    new_tree = tree._register(
+        sample_url_parsed,
+        'dummy_it',
+        register=register_mode
+    )
+
+    assert new_tree is not tree
+
+    if empty_at_end:
+        assert new_tree._by_scheme_and_port == Map()
+    else:
+        assert len(new_tree._by_scheme_and_port) == 1
+        assert type(new_tree._by_scheme_and_port[('http', 80)]) is \
+            MockedTreeBranch
+
+# @pytest.mark.parametrize('register_mode', [True, False])
+# def test_pattern_tree_privatemethod_register(
+#         register_mode,
+#         monkeypatch,
+#         sample_url_parsed
+# ):
+#     """...."""
+#     registered_count = 0
+
+#     def mocked_parse_pattern(url_pattern):
+#         """...."""
+#         assert url_pattern == 'dummy_pattern'
+
+#         for _ in range(2):
+#             yield sample_url_parsed
+
+#     monkeypatch.setattr(pattern_tree, 'parse_pattern', mocked_parse_pattern)
+
+#     def mocked_reconstruct_url(self):
+#         """...."""
+#         return 'dummy_reconstructed_pattern'
+
+#     monkeypatch.setattr(pattern_tree.ParsedUrl, 'reconstruct_url',
+#                         mocked_reconstruct_url)
+
+#     def mocked_register_with_parsed_pattern(
+#             self,
+#             parsed_pat,
+#             wrapped_item,
+#             register=True
+#     ):
+#         """...."""
+#         nonlocal registered_count
+
+#         assert parsed_pat is sample_url_parsed
+#         assert wrapped_item.pattern == 'dummy_reconstructed_pattern'
+#         assert register == register_mode
+
+#         registered_count += 1
+
+#         return 'dummy_new_tree' if registered_count == 2 else dc.replace(self)
+
+#     monkeypatch.setattr(
+#         pattern_tree.PatternTree,
+#         '_register_with_parsed_pattern',
+#         mocked_register_with_parsed_pattern
+#     )
+
+#     pattern_tree = pattern_tree.PatternTree()
+
+#     new_tree = pattern_tree._register(
+#         'dummy_pattern',
+#         'dummy_item',
+#         register_mode
+#     )
+
+#     assert new_tree == 'dummy_new_tree'
+
+@pytest.mark.parametrize('method_name, register_mode', [
+    ('register',   True),
+    ('deregister', False)
+])
+def test_pattern_tree_register(method_name, register_mode, monkeypatch):
+    """...."""
+    def mocked_privatemethod_register(self, parsed_pat, item, register=True):
+        """...."""
+        assert (parsed_pat, item, register) == \
+            ('dummy_pattern', 'dummy_url', register_mode)
+
+        return 'dummy_new_tree'
+
+    monkeypatch.setattr(
+        pattern_tree.PatternTree,
+        '_register',
+        mocked_privatemethod_register
+    )
+
+    method = getattr(pattern_tree.PatternTree(), method_name)
+    assert method('dummy_pattern', 'dummy_url') == 'dummy_new_tree'
+
+@pytest.fixture
+def mock_parse_url(monkeypatch, sample_url_parsed):
+    """...."""
+    def mocked_parse_url(url):
+        """...."""
+        assert url == 'dummy_url'
+        return dc.replace(
+            sample_url_parsed,
+            **getattr(mocked_parse_url, 'url_mod', {})
+        )
+
+    monkeypatch.setattr(pattern_tree, 'parse_url', mocked_parse_url)
+
+    return mocked_parse_url
+
+@pytest.mark.usefixtures('mock_parse_url')
+def test_pattern_tree_search_empty(sample_url_parsed):
+    """...."""
+    for url in ('dummy_url', sample_url_parsed):
+        assert [*pattern_tree.PatternTree().search(url)] == []
+
+@pytest.mark.parametrize('url_mod, out', [
+    ({},
+     ['dummy_set_A', 'dummy_set_B', 'dummy_set_C']),
+
+    ({'has_trailing_slash': True},
+     ['dummy_set_A_with_slash', 'dummy_set_A',
+      'dummy_set_B_with_slash', 'dummy_set_B',
+      'dummy_set_C_with_slash', 'dummy_set_C'])
+])
+def test_pattern_tree_search(
+        url_mod,
+        out,
+        monkeypatch,
+        sample_url_parsed,
+        mock_parse_url,
+):
+    """...."""
+    mock_parse_url.url_mod = url_mod
+
+    dummy_tree_contents = [
+        ['dummy_set_A', 'dummy_set_B'],
+        [],
+        ['dummy_empty_set'] * 3,
+        ['dummy_set_C']
+    ]
+
+    def mocked_filter_by_trailing_slash(items, with_slash):
+        """...."""
+        if items == 'dummy_empty_set':
+            return frozenset()
+
+        return items + ('_with_slash' if with_slash else '')
+
+    monkeypatch.setattr(pattern_tree, 'filter_by_trailing_slash',
+                        mocked_filter_by_trailing_slash)
+
+    class MockedDomainBranch:
+        """...."""
+        def search(self, labels):
+            """...."""
+            assert labels == sample_url_parsed.domain_labels
+
+            for item_sets in dummy_tree_contents:
+                class MockedPathBranch:
+                    """...."""
+                    def search(self, segments, item_sets=item_sets):
+                        """...."""
+                        assert segments == sample_url_parsed.path_segments
+
+                        for dummy_items_set in item_sets:
+                            yield dummy_items_set
+
+                yield MockedPathBranch()
+
+    tree = pattern_tree.PatternTree(
+        _by_scheme_and_port = {('http', 80): MockedDomainBranch()}
+    )
+
+    for url in ('dummy_url', mock_parse_url('dummy_url')):
+        assert [*tree.search(url)] == out
diff --git a/tests/test_server.py b/tests/test_server.py
index 02b9742..854b5f0 100644
--- a/tests/test_server.py
+++ b/tests/test_server.py
@@ -24,9 +24,6 @@
 # file's license. Although I request that you do not make use this code
 # in a proprietary program, I am not going to enforce this in court.
 
-# Enable using with Python 3.7.
-from __future__ import annotations
-
 import pytest
 import sys
 import shutil
@@ -42,9 +39,9 @@ from flask.testing import FlaskClient
 from markupsafe import escape
 from werkzeug import Response
 
-from hydrilla import util as hydrilla_util
+from hydrilla import _version, json_instances
 from hydrilla.builder import Build
-from hydrilla.server import config, _version
+from hydrilla.server import config
 from hydrilla.server.serve import HydrillaApp
 
 here        = Path(__file__).resolve().parent
@@ -125,7 +122,7 @@ def index_json_modification(modify_index_json):
     def handle_index_json(setup):
         """Modify index.json before build."""
         index_path = setup.source_dir / 'index.json'
-        index_json, _ = hydrilla_util.load_instance_from_file(index_path)
+        index_json, _ = json_instances.read_instance(index_path)
 
         index_json = modify_index_json(index_json) or index_json
 
@@ -193,8 +190,8 @@ def test_get_newest(setup: Setup, item_type: str) -> None:
 
     assert ('uuid' in definition) == (setup is not uuidless_setup)
 
-    hydrilla_util.validator_for(f'api_{item_type}_description-1.0.1.schema.json')\
-                 .validate(definition)
+    schema_name = f'api_{item_type}_description-1.0.1.schema.json'
+    json_instances.validator_for(schema_name).validate(definition)
 
 @pytest.mark.parametrize('item_type', ['resource', 'mapping'])
 def test_get_nonexistent(item_type: str) -> None:
@@ -241,8 +238,8 @@ def test_empty_query() -> None:
         'generated_by': expected_generated_by
     }
 
-    hydrilla_util.validator_for('api_query_result-1.0.1.schema.json')\
-                 .validate(response_object)
+    schema_name = 'api_query_result-1.0.1.schema.json'
+    json_instances.validator_for(schema_name).validate(response_object)
 
 def test_query() -> None:
     """
@@ -264,8 +261,8 @@ def test_query() -> None:
         'generated_by': expected_generated_by
     }
 
-    hydrilla_util.validator_for('api_query_result-1.schema.json')\
-                 .validate(response_object)
+    schema_name = 'api_query_result-1.schema.json'
+    json_instances.validator_for(schema_name).validate(response_object)
 
 def test_source() -> None:
     """Verify source descriptions are properly served."""
@@ -282,8 +279,8 @@ def test_source() -> None:
     response = def_get(f'/source/hello.zip')
     assert sha256(response.data).digest().hex() == zipfile_hash
 
-    hydrilla_util.validator_for('api_source_description-1.schema.json')\
-                 .validate(description)
+    schema_name = 'api_source_description-1.schema.json'
+    json_instances.validator_for(schema_name).validate(description)
 
 def test_missing_source() -> None:
     """Verify requests for nonexistent sources result in 404."""
@@ -292,8 +289,3 @@ def test_missing_source() -> None:
 
     response = def_get(f'/source/nonexistent.zip')
     assert response.status_code == 404
-
-def test_normalize_version():
-    assert hydrilla_util.normalize_version([4, 5, 3, 0, 0]) == [4, 5, 3]
-    assert hydrilla_util.normalize_version([1, 0, 5, 0])    == [1, 0, 5]
-    assert hydrilla_util.normalize_version([3, 3])          == [3, 3]
diff --git a/tests/test_url_patterns.py b/tests/test_url_patterns.py
new file mode 100644
index 0000000..c308f18
--- /dev/null
+++ b/tests/test_url_patterns.py
@@ -0,0 +1,188 @@
+# SPDX-License-Identifier: CC0-1.0
+
+# Copyright (C) 2022 Wojtek Kosior <koszko@koszko.org>
+#
+# Available under the terms of Creative Commons Zero v1.0 Universal.
+
+import pytest
+import re
+import dataclasses as dc
+
+from immutables import Map
+
+from hydrilla import url_patterns
+from hydrilla.exceptions import HaketiloException
+
+from .url_patterns_common import *
+
+# @pytest.mark.parametrize('_in, out', [
+#     ({},                           sample_url_str),
+#     ({'path_segments': ()},        'http://example.com'),
+#     ({'has_trailing_slash': True}, 'http://example.com/aa/bb/'),
+#     ({'orig_scheme': 'http*'},     'http*://example.com/aa/bb'),
+#     ({'scheme': 'http_sth'},       'http://example.com/aa/bb'),
+#     ({'port': 443},                'http://example.com:443/aa/bb'),
+
+#     ({'path_segments': (),
+#       'has_trailing_slash': True},
+#      'http://example.com/'),
+
+#     ({'orig_scheme': 'https',
+#       'scheme': 'https',
+#       'port': 443},
+#      'https://example.com/aa/bb'),
+
+#     ({'orig_scheme': 'ftp',
+#       'scheme': 'ftp',
+#       'port': 21},
+#      'ftp://example.com/aa/bb'),
+
+#     ({'orig_scheme': 'file',
+#       'scheme': 'file',
+#       'port': None,
+#       'domain_labels': ()},
+#      'file:///aa/bb')
+# ])
+# def test_reconstruct_parsed_url(_in, out, sample_url_parsed):
+#     """Test the reconstruct_url() method of ParsedUrl class."""
+#     parsed_url = dc.replace(sample_url_parsed, **_in)
+#     assert parsed_url.reconstruct_url() == out
+
+@pytest.mark.parametrize('_in, out', [
+    ({'url': sample_url_str},                    {}),
+    ({'url': 'http://example.com:80/aa/bb'},     {}),
+    ({'url': 'http://example.com//aa///bb'},     {}),
+    ({'url': 'http://example...com/aa/bb'},      {}),
+    ({'url': 'http://example.com/aa/bb?c=d#ef'}, {}),
+    ({'url': 'http://example.com'},              {'path_segments': ()}),
+    ({'url': 'http://example.com/aa/bb/'},       {'has_trailing_slash': True}),
+    ({'url': 'http://example.com:443/aa/bb'},    {'port': 443}),
+
+    ({'url': 'http://example.com/'},
+     {'path_segments': (),
+      'has_trailing_slash': True}),
+
+    ({'url': 'http://example.com/aa/bb',
+      'is_pattern': True,
+      'orig_url': 'http*://example.com/aa/bb/'},
+     {}),
+
+    ({'url': 'https://example.com/aa/bb'},
+     {'scheme': 'https',
+      'port': 443}),
+
+    ({'url': 'ftp://example.com/aa/bb'},
+     {'scheme': 'ftp',
+      'port': 21}),
+
+    ({'url': 'file:///aa/bb'},
+     {'scheme': 'file',
+      'port': None,
+      'domain_labels': ()})
+])
+def test_parse_pattern_or_url(_in, out, sample_url_parsed):
+    """Test normal use (no errors) of the _parse_pattern_or_url() function."""
+    if 'orig_url' not in _in:
+        _in = {**_in, 'orig_url': _in['url']}
+
+    out = {**out, 'orig_url': _in['orig_url']}
+
+    parsed_url = url_patterns._parse_pattern_or_url(**_in)
+    assert parsed_url == dc.replace(sample_url_parsed, **out)
+
+@pytest.mark.parametrize('_in, err', [
+    ({'url': 'file://:78/unexpected/port'},  'err.url_{}.bad'),
+    ({'url': 'file://unexpected.hostname/'}, 'err.url_{}.bad'),
+    ({'url': 'http:///no/hostname'},         'err.url_{}.bad'),
+    ({'url': 'invalid?://example.com'},      'err.url_{}.bad'),
+    ({'url': 'invalid?://example.com',
+      'orig_url': 'invalid?://example.com',
+      'is_pattern': True},
+     'err.url_pattern_{}.bad'),
+
+    ({'url': 'unknown://example.com'}, 'err.url_{}.bad_scheme'),
+    ({'url': 'unknown://example.com',
+      'orig_url': 'unknown://example.com',
+      'is_pattern': True},
+     'err.url_pattern_{}.bad_scheme'),
+
+    ({'url': 'http://example.com:80',
+      'orig_url': 'http*://example.com:80',
+      'is_pattern': True},
+     'err.url_pattern_{}.special_scheme_port'),
+
+    ({'url': 'http://example.com:65536'}, 'err.url_{}.bad_port'),
+    ({'url': 'http://example.com:0'},     'err.url_{}.bad_port'),
+    ({'url': 'http://example.com:65537',
+      'orig_url': 'http://example.com:65537',
+      'is_pattern': True},
+     'err.url_pattern_{}.bad_port'),
+
+    ({'url': 'http://example.com/?a=b',
+      'orig_url': 'http://example.com/?a=b',
+      'is_pattern': True},
+     'err.url_pattern_{}.has_query'),
+
+    ({'url': 'http://example.com/#abc',
+      'orig_url': 'http://example.com/#abc',
+      'is_pattern': True},
+     'err.url_pattern_{}.has_frag')
+])
+def test_parse_pattern_or_url_err(_in, err, sample_url_parsed):
+    """Test error conditions of the _parse_pattern_or_url() function."""
+    if 'orig_url' not in _in:
+        _in = {**_in, 'orig_url': _in['url']}
+
+    err_url = _in['orig_url']
+    err_regex = err.format(re.escape(err_url))
+
+    with pytest.raises(HaketiloException, match=f'^{err_regex}$'):
+        url_patterns._parse_pattern_or_url(**_in)
+
+def test_parse_pattern_or_url_different_urls():
+    """
+    Verify the _parse_pattern_or_url() function allows passed URLs to be
+    different only when parsing a pattern.
+    """
+    urls = [sample_url_str, sample_url_str.replace('http', 'http*')]
+
+    url_patterns._parse_pattern_or_url(*urls, is_pattern=True)
+
+    with pytest.raises(AssertionError):
+        url_patterns._parse_pattern_or_url(*urls)
+
+@pytest.mark.parametrize('_in, out', [
+    ('http://example.com',  ('mocked_pr_http://example.com',)),
+    ('ftp://example.com',   ('mocked_pr_ftp://example.com',)),
+    ('http*://example.com', ('mocked_pr_http://example.com',
+                             'mocked_pr_https://example.com'))
+])
+def test_parse_pattern(monkeypatch, _in, out):
+    """...."""
+    def mocked_parse_pattern_or_url(url, orig_url, is_pattern=False):
+        """...."""
+        assert is_pattern
+        assert orig_url == _in
+
+        return f'mocked_pr_{url}'
+
+    monkeypatch.setattr(url_patterns, '_parse_pattern_or_url',
+                        mocked_parse_pattern_or_url)
+
+    assert url_patterns.parse_pattern(_in) == out
+
+def test_parse_url(monkeypatch):
+    """...."""
+    def mocked_parse_pattern_or_url(url, orig_url):
+        """...."""
+        return f'mocked_pr_{url}'
+
+    monkeypatch.setattr(url_patterns, '_parse_pattern_or_url',
+                        mocked_parse_pattern_or_url)
+
+    assert url_patterns.parse_url('https://example.com') == \
+        'mocked_pr_https://example.com'
+
+def test_parsed_url_hash(sample_url_parsed):
+    """...."""
+    hash(sample_url_parsed)
diff --git a/tests/test_versions.py b/tests/test_versions.py
new file mode 100644
index 0000000..43a3f33
--- /dev/null
+++ b/tests/test_versions.py
@@ -0,0 +1,41 @@
+# SPDX-License-Identifier: CC0-1.0
+
+# Copyright (C) 2022 Wojtek Kosior <koszko@koszko.org>
+#
+# Available under the terms of Creative Commons Zero v1.0 Universal.
+
+import pytest
+
+from hydrilla import versions
+
+sample_version_tuples  = [(4, 5, 3), (1, 0, 5), (3,)]
+sample_version_strings = ['4.5.3',   '1.0.5',   '3']
+
+sample_versions = [*zip(sample_version_tuples, sample_version_strings)]
+
+@pytest.mark.parametrize('version_tuple', sample_version_tuples)
+def test_normalize_version(version_tuple):
+    """Verify that normalize_version() produces proper results."""
+    assert versions.normalize_version([*version_tuple])    == version_tuple
+    assert versions.normalize_version([*version_tuple, 0]) == version_tuple
+
+@pytest.mark.parametrize('version_tuple, string', sample_versions)
+def test_parse_version(version_tuple, string):
+    """Verify that parse_version() produces proper results."""
+    assert versions.parse_version(string)
+    assert versions.parse_version(string + '.0') == tuple([*version_tuple, 0])
+
+def test_parse_version_bad_string():
+    """Verify that parse_version() raises when passed an invalid string."""
+    with pytest.raises(ValueError):
+        versions.parse_version('i am not a valid version')
+
+@pytest.mark.parametrize('version_tuple, string', sample_versions)
+def test_version_string(version_tuple, string):
+    """Verify that version_string() produces proper results."""
+    for _version_tuple, _string in [
+            (version_tuple,              string),
+            (tuple([*version_tuple, 0]), f'{string}.0')
+    ]:
+        assert versions.version_string(_version_tuple)    == _string
+        assert versions.version_string(_version_tuple, 5) == f'{_string}-5'
diff --git a/tests/url_patterns_common.py b/tests/url_patterns_common.py
new file mode 100644
index 0000000..de6651d
--- /dev/null
+++ b/tests/url_patterns_common.py
@@ -0,0 +1,23 @@
+# SPDX-License-Identifier: CC0-1.0
+
+# Copyright (C) 2022 Wojtek Kosior <koszko@koszko.org>
+#
+# Available under the terms of Creative Commons Zero v1.0 Universal.
+
+import pytest
+
+from hydrilla import url_patterns
+
+sample_url_str = 'http://example.com/aa/bb'
+
+@pytest.fixture(scope='session')
+def sample_url_parsed():
+    """Generate a simple ParsedUrl object."""
+    return url_patterns.ParsedUrl(
+        orig_url           = sample_url_str,
+        scheme             = 'http',
+        domain_labels      = ('com', 'example'),
+        path_segments      = ('aa', 'bb'),
+        has_trailing_slash = False,
+        port               = 80
+    )