tests: add asar comparator

tests/comparators/test_asar.py

+#
+# diffoscope: in-depth comparison of files, archives, and directories
+#
+# Copyright © 2015 Jérémy Bobbio <lunar@debian.org>
+# Copyright © 2015-2017, 2020 Chris Lamb <lamby@debian.org>
+#
+# diffoscope is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# diffoscope is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with diffoscope.  If not, see <https://www.gnu.org/licenses/>.
+
+import pytest
+
+from diffoscope.config import Config
+from diffoscope.comparators.asar import AsarFile
+from diffoscope.comparators.missing_file import MissingFile
+
+from ..utils.data import load_fixture, get_data
+from ..utils.tools import skip_unless_tools_exist
+from ..utils.nonexisting import assert_non_existing
+
+
+asar1 = load_fixture("test1.asar")
+asar2 = load_fixture("test2.asar")
+
+
+def test_identification(asar1):
+    assert isinstance(asar1, AsarFile)
+
+
+def test_no_differences(asar1):
+    difference = asar1.compare(asar1)
+    assert difference is None
+
+
+@pytest.fixture
+def differences(asar1, asar2):
+    return asar1.compare(asar2).details
+
+
+@skip_unless_tools_exist("asar")
+def test_text_file(differences):
+    assert differences[0].source1 == "dir/text"
+    assert differences[0].source2 == "dir/text"
+    expected_diff = get_data("text_ascii_expected_diff")
+    assert differences[0].unified_diff == expected_diff