add missing english translations and verify message texts of raised exceptions in tests

6 files changed, 269 insertions, 87 deletions

diff --git a/conftest.py b/conftest.py
index 141cba5..65d13d5 100644
--- a/conftest.py
+++ b/conftest.py
@@ -8,6 +8,7 @@ import sys
 from pathlib import Path
 
 import pytest
+import pkgutil
 
 here = Path(__file__).resolve().parent
 sys.path.insert(0, str(here / 'src'))
@@ -34,3 +35,35 @@ def mock_subprocess_run(monkeypatch, request):
         run = mocked_run
 
     monkeypatch.setattr(where, 'subprocess', MockedSubprocess)
+
+@pytest.fixture(autouse=True)
+def no_gettext(monkeypatch, request):
+    """
+    Make gettext return all strings untranslated unless we request otherwise.
+    """
+    if request.node.get_closest_marker('enable_gettext'):
+        return
+
+    import hydrilla
+    modules_to_process = [hydrilla]
+
+    def add_child_modules(parent):
+        """
+        Recursuvely collect all modules descending from 'parent' into an array.
+        """
+        try:
+            load_paths = parent.__path__
+        except AttributeError:
+            return
+
+        for module_info in pkgutil.iter_modules(load_paths):
+            if module_info.name != '__main__':
+                __import__(f'{parent.__name__}.{module_info.name}')
+                modules_to_process.append(getattr(parent, module_info.name))
+                add_child_modules(getattr(parent, module_info.name))
+
+    add_child_modules(hydrilla)
+
+    for module in modules_to_process:
+        if hasattr(module, '_'):
+            monkeypatch.setattr(module, '_', lambda message: message)
diff --git a/src/hydrilla/builder/build.py b/src/hydrilla/builder/build.py
index ce4935c..feecdfe 100644
--- a/src/hydrilla/builder/build.py
+++ b/src/hydrilla/builder/build.py
@@ -83,10 +83,11 @@ def generate_spdx_report(root: Path) -> bytes:
         try:
             cp = subprocess.run(command, capture_output=True, text=True)
         except FileNotFoundError:
-            raise ReuseError(_('couldnt_execute_reuse_is_it_installed'))
+            msg = _('couldnt_execute_{}_is_it_installed').format('reuse')
+            raise ReuseError(msg)
 
         if cp.returncode != 0:
-            msg = _('reuse_command_{}_failed').format(' '.join(command))
+            msg = _('command_{}_failed').format(' '.join(command))
             raise ReuseError(msg, cp)
 
     return cp.stdout.encode()
diff --git a/src/hydrilla/builder/local_apt.py b/src/hydrilla/builder/local_apt.py
index 8382af8..4c93a4d 100644
--- a/src/hydrilla/builder/local_apt.py
+++ b/src/hydrilla/builder/local_apt.py
@@ -114,10 +114,11 @@ class Apt:
         try:
             cp = run(command, **kwargs)
         except FileNotFoundError:
-            raise AptError(_('couldnt_execute_apt_get_is_it_installed'))
+            msg = _('couldnt_execute_{}_is_it_installed').format('apt-get')
+            raise AptError(msg)
 
         if cp.returncode != 0:
-            msg = _('apt_get_command_{}_failed').format(' '.join(command))
+            msg = _('command_{}_failed').format(' '.join(command))
             raise AptError(msg, cp)
 
         return cp
@@ -185,7 +186,7 @@ def apt_keyring(keys: [str]) -> bytes:
     try:
         from gnupg import GPG
     except ModuleNotFoundError:
-        raise GpgError(_('couldnt_import_gnupg_is_it_installed'))
+        raise GpgError(_('couldnt_import_{}_is_it_installed').format('gnupg'))
 
     gpg = GPG(keyring=str(cache_dir() / 'master_keyring.gpg'))
     for key in keys:
@@ -193,7 +194,7 @@ def apt_keyring(keys: [str]) -> bytes:
             continue
 
         if gpg.recv_keys(default_keyserver, key).imported == 0:
-            raise GpgError(_('gpg_couldnt_recv_key'))
+            raise GpgError(_('gpg_couldnt_recv_key_{}').format(key))
 
     return gpg.export_keys(keys, armor=False, minimal=True)
 
@@ -404,10 +405,11 @@ def piggybacked_system(piggyback_def: dict, foreign_packages: Optional[Path]) \
             try:
                 cp = run(command)
             except FileNotFoundError:
-                raise AptError(_('couldnt_execute_dpkg_deb_is_it_installed'))
+                msg = _('couldnt_execute_{}_is_it_installed'.format('dpkg-deb'))
+                raise AptError(msg)
 
             if cp.returncode != 0:
-                msg = _('dpkg_deb_command_{}_failed').format(' '.join(command))
+                msg = _('command_{}_failed').format(' '.join(command))
                 raise AptError(msg, cp)
 
         docs_dir = root / 'usr' / 'share' / 'doc'
diff --git a/src/hydrilla/builder/locales/en_US/LC_MESSAGES/hydrilla-messages.po b/src/hydrilla/builder/locales/en_US/LC_MESSAGES/hydrilla-messages.po
index e3ab525..a6c6e83 100644
--- a/src/hydrilla/builder/locales/en_US/LC_MESSAGES/hydrilla-messages.po
+++ b/src/hydrilla/builder/locales/en_US/LC_MESSAGES/hydrilla-messages.po
@@ -7,7 +7,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: hydrilla.builder 0.1.dev16+g4e46d7f.d20220211\n"
 "Report-Msgid-Bugs-To: koszko@koszko.org\n"
-"POT-Creation-Date: 2022-04-19 13:51+0200\n"
+"POT-Creation-Date: 2022-05-10 16:47+0200\n"
 "PO-Revision-Date: 2022-02-12 00:00+0000\n"
 "Last-Translator: Wojtek Kosior <koszko@koszko.org>\n"
 "Language: en_US\n"
@@ -18,45 +18,63 @@ msgstr ""
 "Content-Transfer-Encoding: 8bit\n"
 "Generated-By: Babel 2.8.0\n"
 
-#: src/hydrilla/builder/build.py:118
-msgid "couldnt_import_reuse_is_it_installed"
-msgstr ""
-"Could not import 'reuse'. Is the tool installed and visible to this "
-"Python instance?"
+#: src/hydrilla/builder/build.py:86 src/hydrilla/builder/local_apt.py:117
+#: src/hydrilla/builder/local_apt.py:408
+msgid "couldnt_execute_{}_is_it_installed"
+msgstr "Could not execute '{}'. Is the tool installed and reachable via PATH?"
+
+#: src/hydrilla/builder/build.py:90 src/hydrilla/builder/local_apt.py:121
+#: src/hydrilla/builder/local_apt.py:412
+msgid "command_{}_failed"
+msgstr "The following command finished execution with a non-zero exit status: {}"
 
-#: src/hydrilla/builder/build.py:123
-msgid "spdx_report_from_reuse_incompliant"
-msgstr "Attempt to generate an SPDX report for a REUSE-incompliant package."
+#: src/hydrilla/builder/build.py:198
+msgid "path_contains_double_dot_{}"
+msgstr ""
+"Attempt to load '{}' which includes a forbidden parent reference ('..') "
+"in the path."
 
-#: src/hydrilla/builder/build.py:207
+#: src/hydrilla/builder/build.py:205
 msgid "loading_{}_outside_package_dir"
 msgstr "Attempt to load '{}' which lies outside package source directory."
 
-#: src/hydrilla/builder/build.py:211
+#: src/hydrilla/builder/build.py:209
 msgid "loading_reserved_index_json"
 msgstr "Attempt to load 'index.json' which is a reserved filename."
 
-#: src/hydrilla/builder/build.py:329
+#: src/hydrilla/builder/build.py:350
 msgid "report_spdx_not_in_copyright_list"
 msgstr ""
 "Told to generate 'report.spdx' but 'report.spdx' is not listed among "
 "copyright files. Refusing to proceed."
 
-#: src/hydrilla/builder/build.py:402
+#: src/hydrilla/builder/build.py:421
+msgid "build_package_from_srcdir_to_dstdir"
+msgstr ""
+"Build Hydrilla package from `scrdir` and write the resulting files under "
+"`dstdir`."
+
+#: src/hydrilla/builder/build.py:423
 msgid "source_directory_to_build_from"
 msgstr "Source directory to build from."
 
-#: src/hydrilla/builder/build.py:404
+#: src/hydrilla/builder/build.py:425
 msgid "path_instead_of_index_json"
 msgstr ""
 "Path to file to be processed instead of index.json (if not absolute, "
 "resolved relative to srcdir)."
 
-#: src/hydrilla/builder/build.py:406
+#: src/hydrilla/builder/build.py:427
+msgid "path_instead_for_piggyback_files"
+msgstr ""
+"Path to a non-standard directory with foreign packages' archive files to "
+"use."
+
+#: src/hydrilla/builder/build.py:429
 msgid "built_package_files_destination"
 msgstr "Destination directory to write built package files to."
 
-#: src/hydrilla/builder/build.py:408
+#: src/hydrilla/builder/build.py:431
 #, python-format
 msgid "%(prog)s_%(version)s_license"
 msgstr ""
@@ -67,15 +85,45 @@ msgstr ""
 "This is free software: you are free to change and redistribute it.\n"
 "There is NO WARRANTY, to the extent permitted by law."
 
-#: src/hydrilla/builder/build.py:409
+#: src/hydrilla/builder/build.py:432
 msgid "version_printing"
 msgstr "Print version information and exit."
 
-#: src/hydrilla/builder/build.py:415
-msgid "build_package_from_srcdir_to_dstdir"
+#: src/hydrilla/builder/common_errors.py:62
+msgid "STDOUT_OUTPUT_heading"
+msgstr "## Command's standard output ##"
+
+#: src/hydrilla/builder/common_errors.py:65
+msgid "STDERR_OUTPUT_heading"
+msgstr "## Command's standard error output ##"
+
+#: src/hydrilla/builder/local_apt.py:146
+msgid "distro_{}_unknown"
+msgstr "Attempt to use an unknown software distribution '{}'."
+
+#: src/hydrilla/builder/local_apt.py:189
+msgid "couldnt_import_{}_is_it_installed"
 msgstr ""
-"Build Hydrilla package from `scrdir` and write the resulting files under "
-"`dstdir`."
+"Could not import '{}'. Is the module installed and visible to this Python"
+" instance?"
+
+#: src/hydrilla/builder/local_apt.py:197
+msgid "gpg_couldnt_recv_key_{}"
+msgstr "Could not import PGP key '{}'."
+
+#: src/hydrilla/builder/local_apt.py:314
+msgid "apt_install_output_not_understood"
+msgstr "The output of an 'apt-get install' command was not understood."
+
+#: src/hydrilla/builder/local_apt.py:342
+msgid "apt_download_gave_bad_filename_{}"
+msgstr "The 'apt-get download' command produced a file with unexpected name '{}'."
+
+#: src/hydrilla/builder/piggybacking.py:102
+msgid "loading_{}_outside_piggybacked_dir"
+msgstr ""
+"Attempt to load '{}' which lies outside piggybacked packages files root "
+"directory."
 
 #: src/hydrilla/util/_util.py:79
 msgid "bad_comment"
diff --git a/tests/test_build.py b/tests/test_build.py
index a30cff4..77b1898 100644
--- a/tests/test_build.py
+++ b/tests/test_build.py
@@ -582,49 +582,64 @@ 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 FileNotFoundError
+    return FileNotFoundError,
 
 @error_maker
 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
+    return ValidationError,
 
 @error_maker
 def sample_source_error_bad_comment(monkeypatch, sample_source):
     """Modify index.json to have an invalid '/' in it."""
-    return json.JSONDecodeError, json.dumps(index_obj) + '/something\n'
+    return json.JSONDecodeError, '^bad_comment: .*', \
+        json.dumps(index_obj) + '/something\n'
 
 @error_maker
 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'
+    return json.JSONDecodeError, '', json.dumps(index_obj) + '???\n'
 
 @error_maker
 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
+    return build.ReuseError, '^couldnt_execute_reuse_is_it_installed$'
 
 @error_maker
 def sample_source_error_missing_license(monkeypatch, sample_source):
     """Remove a file to make package REUSE-incompliant."""
     (sample_source / 'README.txt.license').unlink()
-    return build.ReuseError
+
+    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
 
 @error_maker
 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
+    return FileReferenceError, '^path_contains_double_dot_\\.\\./abc$'
 
 @error_maker
 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
+    return FileReferenceError, '^loading_reserved_index_json$'
 
 @error_maker
 def sample_source_error_report_excluded(monkeypatch, sample_source):
@@ -635,7 +650,7 @@ def sample_source_error_report_excluded(monkeypatch, sample_source):
     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
+    return FileReferenceError, '^report_spdx_not_in_copyright_list$'
 
 @pytest.fixture(params=error_makers)
 def sample_source_make_errors(request, monkeypatch, sample_source):
@@ -644,10 +659,8 @@ def sample_source_make_errors(request, monkeypatch, sample_source):
     broken versions. Return an error type that should be raised when running
     test build.
     """
-    index_text = None
-    error_type = request.param(monkeypatch, sample_source)
-    if type(error_type) is tuple:
-        error_type, index_text = error_type
+    error_type, error_regex, index_text = \
+        [*request.param(monkeypatch, sample_source), '', ''][0:3]
 
     index_text = index_text or json.dumps(index_obj)
 
@@ -655,13 +668,13 @@ def sample_source_make_errors(request, monkeypatch, sample_source):
 
     monkeypatch.setitem(src_files, 'index.json', index_text.encode())
 
-    return error_type
+    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 = sample_source_make_errors
+    error_type, error_regex = sample_source_make_errors
 
     dstdir = Path(tmpdir) / 'dstdir'
     tmpdir = Path(tmpdir) / 'example'
@@ -669,6 +682,6 @@ def test_build_error(tmpdir, sample_source, sample_source_make_errors):
     dstdir.mkdir(exist_ok=True)
     tmpdir.mkdir(exist_ok=True)
 
-    with pytest.raises(error_type):
+    with pytest.raises(error_type, match=error_regex):
         build.Build(sample_source, Path('index.json'))\
              .write_package_files(dstdir)
diff --git a/tests/test_local_apt.py b/tests/test_local_apt.py
index 4f3a831..1ff52cc 100644
--- a/tests/test_local_apt.py
+++ b/tests/test_local_apt.py
@@ -290,14 +290,11 @@ def test_local_apt_missing(mock_cache_dir):
     """
     sources_list = local_apt.SourcesList(['deb-src sth', 'deb sth'])
 
-    with pytest.raises(local_apt.AptError) as excinfo:
+    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
 
-    assert len(excinfo.value.args) == 1
-    assert isinstance(excinfo.value.args[0], str)
-    assert '\n' not in excinfo.value.args[0]
-
 @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):
@@ -307,14 +304,22 @@ def test_local_apt_update_fail(mock_cache_dir):
     """
     sources_list = local_apt.SourcesList(['deb-src sth', 'deb sth'])
 
-    with pytest.raises(local_apt.AptError) as excinfo:
-        with local_apt.local_apt(sources_list, local_apt.default_keys) as apt:
-            pass
+    error_regex = """^\
+command_apt-get -c \\S+ update_failed
+
+STDOUT_OUTPUT_heading
+
+some output
 
-    assert len(excinfo.value.args) == 1
+STDERR_OUTPUT_heading
 
-    assert re.match(r'.*\n\n.*\n\nsome output\n\n.*\n\nsome error output',
-                    excinfo.value.args[0])
+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')
@@ -359,17 +364,24 @@ def test_local_apt_install_fail(mock_cache_dir):
     destination = mock_cache_dir / 'destination'
     destination.mkdir()
 
-    with pytest.raises(local_apt.AptError) as excinfo:
+    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 len(excinfo.value.args) == 1
-
-    assert re.match(r'^.*\n\n.*\n\n', excinfo.value.args[0])
-    assert re.search(r'\n\nsome error output$', excinfo.value.args[0])
-    assert sample_install_stdout in excinfo.value.args[0]
-
     assert [*destination.iterdir()] == []
 
 @pytest.mark.subprocess_run(local_apt, make_run_apt_get(download_code=1))
@@ -383,14 +395,73 @@ def test_local_apt_download_fail(mock_cache_dir):
     destination = mock_cache_dir / 'destination'
     destination.mkdir()
 
-    with pytest.raises(local_apt.AptError) as excinfo:
+    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)
 
-    assert len(excinfo.value.args) == 1
+    assert [*destination.iterdir()] == []
 
-    assert re.match(r'.*\n\n.*\n\nsome output\n\n.*\n\nsome error output',
-                    excinfo.value.args[0])
+@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)
 
     assert [*destination.iterdir()] == []
 
@@ -405,14 +476,22 @@ def test_local_apt_source_fail(mock_cache_dir):
     destination = mock_cache_dir / 'destination'
     destination.mkdir()
 
-    with pytest.raises(local_apt.AptError) as excinfo:
-        local_apt.download_apt_packages(sources_list, local_apt.default_keys,
-                                        ['libjs-mathjax'], destination)
+    error_regex = """^\
+command_apt-get -c \\S* source --download-only \\S+_failed
+
+STDOUT_OUTPUT_heading
 
-    assert len(excinfo.value.args) == 1
+some output
 
-    assert re.match(r'.*\n\n.*\n\nsome output\n\n.*\n\nsome error output',
-                    excinfo.value.args[0])
+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)
 
     assert [*destination.iterdir()] == []
 
@@ -421,7 +500,7 @@ def test_sources_list():
     list = local_apt.SourcesList([], 'nabia')
     assert list.identity() == 'nabia'
 
-    with pytest.raises(local_apt.DistroError):
+    with pytest.raises(local_apt.DistroError, match='^distro_nabiał_unknown$'):
         local_apt.SourcesList([], 'nabiał')
 
     list = local_apt.SourcesList(['deb sth', 'deb-src sth'], 'nabia')
@@ -557,7 +636,9 @@ def test_piggybacked_system_download(params):
         assert piggybacked.resolve_file(PurePosixPath('a/b/c')) == None
         assert piggybacked.resolve_file(PurePosixPath('')) == None
 
-        with pytest.raises(FileReferenceError):
+        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
@@ -615,7 +696,8 @@ 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) as excinfo:
+    with pytest.raises(local_apt.AptError,
+                       match='^couldnt_execute_dpkg-deb_is_it_installed$'):
         with local_apt.piggybacked_system({
                 'system': 'apt',
                 'distribution': 'nabia',
@@ -624,11 +706,6 @@ def test_piggybacked_system_missing():
         }, None) as piggybacked:
             pass
 
-    assert len(excinfo.value.args) == 1
-
-    assert '\n' not in excinfo.value.args[0]
-
-
 @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():
@@ -636,7 +713,20 @@ def test_piggybacked_system_fail():
     Verify that the piggybacked_system() function raises a proper error when
     'dpkg-deb -x' command returns non-0.
     """
-    with pytest.raises(local_apt.AptError) as excinfo:
+    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',
@@ -644,8 +734,3 @@ def test_piggybacked_system_fail():
                 'dependencies': False
         }, None) as piggybacked:
             pass
-
-    assert len(excinfo.value.args) == 1
-
-    assert re.match(r'.*\n\n.*\n\nsome output\n\n.*\n\nsome error output',
-                    excinfo.value.args[0])