Merge pull request #37 from joseph-roitman/unsupported-values-error

Useful unsupported values errors

pytest_snapshot/plugin.py

@@ -48,6 +48,14 @@ def _file_encode(string: str) -> bytes:
     Returns the bytes that would be in a file created using ``path.write_text(string)``.
     See universal newlines documentation.
     """
+    if '\r' in string:
+        raise ValueError('''\
+Snapshot testing strings containing "\\r" is not supported.
+To snapshot test non-standard newlines you should convert the tested value to bytes.
+Warning: git may decide to modify the newlines in the snapshot file.
+To avoid this read \
+https://docs.github.com/en/get-started/getting-started-with-git/configuring-git-to-handle-line-endings''')
+
     return string.replace('\n', os.linesep).encode()
 
 
@@ -153,25 +161,27 @@ def assert_match(self, value: Union[str, bytes], snapshot_name: Union[str, Path]
 
         if snapshot_path.is_file():
             encoded_expected_value = snapshot_path.read_bytes()
-            expected_value = decode(encoded_expected_value)
         elif snapshot_path.exists():
             raise AssertionError('snapshot exists but is not a file: {}'.format(shorten_path(snapshot_path)))
         else:
             encoded_expected_value = None
-            expected_value = None
 
         if self._snapshot_update:
             encoded_value = encode(value)
-            snapshot_path.parent.mkdir(parents=True, exist_ok=True)
-            if encoded_expected_value is not None:
-                if encoded_expected_value != encoded_value:
-                    snapshot_path.write_bytes(encoded_value)
-                    self._updated_snapshots.append(snapshot_path)
-            else:
+            if encoded_expected_value is None or encoded_value != encoded_expected_value:
+                decoded_encoded_value = decode(encoded_value)
+                if decoded_encoded_value != value:
+                    raise ValueError("value is not supported by pytest-snapshot's serializer.")
+
+                snapshot_path.parent.mkdir(parents=True, exist_ok=True)
                 snapshot_path.write_bytes(encoded_value)
-                self._created_snapshots.append(snapshot_path)
+                if encoded_expected_value is None:
+                    self._created_snapshots.append(snapshot_path)
+                else:
+                    self._updated_snapshots.append(snapshot_path)
         else:
             if encoded_expected_value is not None:
+                expected_value = decode(encoded_expected_value)
                 try:
                     compare(value, expected_value)
                 except AssertionError as e:

tests/test_assert_match.py

@@ -3,6 +3,7 @@
 
 import pytest
 
+from pytest_snapshot.plugin import _file_encode
 from tests.utils import assert_pytest_passes
 
 
@@ -301,3 +302,79 @@ def test_sth(snapshot):
     assert encoded_snapshot == expected_encoded_snapshot
 
     assert_pytest_passes(testdir)  # assert that snapshot update worked
+
+
+def test_assert_match_unsupported_value_existing_snapshot(testdir, basic_case_dir):
+    """
+    Test that when running tests without --snapshot-update, we don't tell the user that the value is unsupported.
+    We instead tell the user that the value does not equal the snapshot. This behaviour is more helpful.
+    """
+    basic_case_dir.join('newline.txt').write_binary(_file_encode('\n'))
+    testdir.makepyfile(r"""
+        def test_sth(snapshot):
+            snapshot.snapshot_dir = 'case_dir'
+            snapshot.assert_match('\r', 'newline.txt')
+    """)
+    result = testdir.runpytest('-v')
+    result.stdout.fnmatch_lines([
+        '*::test_sth FAILED*',
+        'E* AssertionError: value does not match the expected value in snapshot case_dir?newline.txt',
+        "E* - '\\n'",
+        "E* + '\\r'",
+    ])
+    assert result.ret == 1
+
+
+def test_assert_match_unsupported_value_update_existing_snapshot(testdir, basic_case_dir):
+    basic_case_dir.join('newline.txt').write_binary(_file_encode('\n'))
+    testdir.makepyfile(r"""
+        import os
+        from unittest import mock
+        def _file_encode(string: str) -> bytes:
+            return string.replace('\n', os.linesep).encode()
+        
+        def test_sth(snapshot):
+            snapshot.snapshot_dir = 'case_dir'
+            with mock.patch('pytest_snapshot.plugin._file_encode', _file_encode):
+                snapshot.assert_match('\r', 'newline.txt')
+    """)
+    result = testdir.runpytest('-v', '--snapshot-update')
+    result.stdout.fnmatch_lines([
+        '*::test_sth FAILED*',
+        "E* ValueError: value is not supported by pytest-snapshot's serializer.",
+    ])
+    assert result.ret == 1
+
+
+def test_assert_match_unsupported_value_create_snapshot(testdir, basic_case_dir):
+    testdir.makepyfile(r"""
+        import os
+        from unittest import mock
+        def _file_encode(string: str) -> bytes:
+            return string.replace('\n', os.linesep).encode()
+        
+        def test_sth(snapshot):
+            snapshot.snapshot_dir = 'case_dir'
+            with mock.patch('pytest_snapshot.plugin._file_encode', _file_encode):
+                snapshot.assert_match('\r', 'newline.txt')
+    """)
+    result = testdir.runpytest('-v', '--snapshot-update')
+    result.stdout.fnmatch_lines([
+        '*::test_sth FAILED*',
+        "E* ValueError: value is not supported by pytest-snapshot's serializer.",
+    ])
+    assert result.ret == 1
+
+
+def test_assert_match_unsupported_value_slash_r(testdir, basic_case_dir):
+    testdir.makepyfile(r"""
+        def test_sth(snapshot):
+            snapshot.snapshot_dir = 'case_dir'
+            snapshot.assert_match('\r', 'newline.txt')
+    """)
+    result = testdir.runpytest('-v', '--snapshot-update')
+    result.stdout.fnmatch_lines([
+        '*::test_sth FAILED*',
+        'E* ValueError: Snapshot testing strings containing "\\r" is not supported.'
+    ])
+    assert result.ret == 1