New upstream version 1.1~beta1upstream/1.1_beta1debian-upstream

1 files changed, 754 insertions, 0 deletions

diff --git a/tests/test_local_apt.py b/tests/test_local_apt.py
new file mode 100644
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--- /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