Merge pull request #50 from joseph-roitman/assert-plain

Test --assert=plain behaviour and fix related bug.

pytest_snapshot/plugin.py

@@ -188,7 +188,7 @@ def assert_match(self, value: Union[str, bytes], snapshot_name: Union[str, Path]
                 else:
                     snapshot_diff_msg = None
 
-                if snapshot_diff_msg:
+                if snapshot_diff_msg is not None:
                     snapshot_diff_msg = 'value does not match the expected value in snapshot {}\n{}'.format(
                         shorten_path(snapshot_path), snapshot_diff_msg)
                     raise AssertionError(snapshot_diff_msg)
@@ -255,6 +255,6 @@ def _get_default_snapshot_dir(node: _pytest.python.Function) -> Path:
         parametrize_name = parametrize_match.group(1)
         parametrize_name = get_valid_filename(parametrize_name)
     default_snapshot_dir = test_module_dir.join('snapshots', test_module, test_name)
-    if parametrize_name:
+    if parametrize_name is not None:
         default_snapshot_dir = default_snapshot_dir.join(parametrize_name)
     return Path(str(default_snapshot_dir))

tests/test_assert_match.py

@@ -3,6 +3,7 @@
 
 import pytest
 
+from pytest_snapshot._utils import simple_version_parse
 from pytest_snapshot.plugin import _file_encode
 from tests.utils import assert_pytest_passes
 
@@ -90,6 +91,37 @@ def test_sth(snapshot):
     assert result.ret == 1
 
 
+@pytest.mark.skipif(simple_version_parse(pytest.__version__) < (5, 0, 0), reason="consecutive flag not supported.")
+def test_assert_match_failure_assert_plain(testdir, basic_case_dir):
+    """
+    Testing plugin behavior when users run "pytest --assert=plain" is complicated and fragile since the outer pytest
+    and inner pytest affect one another. To get around this, we mock "--assert=plain" behavior.
+    """
+    testdir.makepyfile(r"""
+        from unittest import mock
+        def _assert_equal_mock(value, snapshot):
+            raise AssertionError()
+
+        def test_sth(snapshot):
+            snapshot.snapshot_dir = 'case_dir'
+            with mock.patch('pytest_snapshot.plugin._assert_equal', _assert_equal_mock):
+                snapshot.assert_match('the INCORRECT value of snapshot1.txt\n', 'snapshot1.txt')
+    """)
+
+    result = testdir.runpytest('-v')
+    result.stdout.fnmatch_lines([
+        '*::test_sth FAILED*',
+    ])
+    # Use consecutive=True to verify that the mock was not accidentally broken.
+    result.stdout.fnmatch_lines([
+        ">* raise AssertionError(snapshot_diff_msg)",
+        'E* AssertionError: value does not match the expected value in snapshot case_dir?snapshot1.txt',
+        '',
+        '*plugin.py:*: AssertionError',
+    ], consecutive=True)
+    assert result.ret == 1
+
+
 def test_assert_match_invalid_type(testdir, basic_case_dir):
     testdir.makepyfile(r"""
         def test_sth(snapshot):

tox.ini

@@ -1,7 +1,7 @@
 # For more information about tox, see https://tox.readthedocs.io/en/latest/
 [tox]
 envlist =
-    # Pytest <6 doesn't work on Python >=3.10
+    # Pytest <6.2.5 not supported on Python >=3.10
     py{36,37,38,39}-pytest{3,4,5}-coverage
     py{35,36,37,38,39,310,3}-pytest{6,}-coverage
     # Coverage is slow in pypy