add white_space_dot to config

pytest_examples/config.py

@@ -27,6 +27,8 @@ class ExamplesConfig:
     ruff_line_length: int | None = None
     ruff_select: list[str] | None = None
     ruff_ignore: list[str] | None = None
+    white_space_dot: bool = False
+    """If True, replace spaces with `·` in example diffs."""
 
     def black_mode(self):
         return BlackMode(

pytest_examples/lint.py

@@ -81,16 +81,22 @@ def black_format(source: str, config: ExamplesConfig, *, remove_double_blank: bo
 def black_check(example: CodeExample, config: ExamplesConfig) -> None:
     after_black = black_format(example.source, config, remove_double_blank=example.in_py_file())
     if example.source != after_black:
-        diff = code_diff(example, after_black)
+        diff = code_diff(example, after_black, config.white_space_dot)
         raise FormatError(f'black failed:\n{indent(diff, "  ")}')
 
 
-def code_diff(example: CodeExample, after: str) -> str:
-    diff = black_diff(example.source, after, 'before', 'after')
+def code_diff(example: CodeExample, after: str, white_space_dot: bool) -> str:
+    diff = black_diff(sub_space(example.source, white_space_dot), sub_space(after, white_space_dot), 'before', 'after')
 
     def replace_at_line(match: re.Match) -> str:
         offset = re.sub(r'\d+', lambda m: str(int(m.group(0)) + example.start_line), match.group(2))
         return f'{match.group(1)}{offset}{match.group(3)}'
 
-    # we could add `.replace(' ', '·')` to make white space easier to understand
     return re.sub(r'^(@@\s*)(.*)(\s*@@)$', replace_at_line, diff, flags=re.M)
+
+
+def sub_space(text: str, white_space_dot: bool) -> str:
+    if white_space_dot:
+        return text.replace(' ', '·')
+    else:
+        return text

pytest_examples/run_code.py

@@ -174,15 +174,16 @@ def __exit__(self, *args) -> None:
             self.patch.stop()
 
     def check_print_statements(self, example: CodeExample) -> None:
-        with_prints = self._insert_print_statements(example)
-        # we check against the raw `with_prints` and `with_prints` with trailing whitespace removed
-        if example.source != with_prints and example.source != re.sub(r'[ \t]+\n', '\n', with_prints):
-            diff = code_diff(example, with_prints)
+        new_code = self.updated_print_statements(example)
+        if new_code is not None:
+            diff = code_diff(example, new_code, self.config.white_space_dot)
             pytest.fail(f'Print output changed code:\n{indent(diff, "  ")}', pytrace=False)
 
     def updated_print_statements(self, example: CodeExample) -> str | None:
         with_prints = self._insert_print_statements(example)
-        if example.source != with_prints:
+        # we check against the raw `with_prints` and `with_prints` with trailing whitespace removed
+        # since trailing white space will have already been stripped by pre-commit in `example.source`
+        if example.source not in (with_prints, re.sub(r'[ \t]+\n', '\n', with_prints)):
             return with_prints
 
     def print_statements(self) -> list[PrintStatement]:

tests/test_run_examples.py

@@ -174,6 +174,40 @@ def test_find_run_examples(example: CodeExample, eval_example: EvalExample):
     ]
 
 
+def test_black_error_dot_space(pytester: pytest.Pytester):
+    pytester.makefile(
+        '.md',
+        my_file='line 1\nline 2\n```py\nx =[1,2, 3]\n```',
+    )
+    # language=Python
+    pytester.makepyfile(
+        """
+from pytest_examples import find_examples, CodeExample, EvalExample
+import pytest
+
+@pytest.mark.parametrize('example', find_examples('.'), ids=str)
+def test_find_run_examples(example: CodeExample, eval_example: EvalExample):
+    eval_example.config.white_space_dot = True
+    eval_example.lint_black(example)
+"""
+    )
+
+    result = pytester.runpytest('-p', 'no:pretty', '-v')
+    result.assert_outcomes(failed=1)
+
+    failures_start = next(index for index, line in enumerate(result.outlines) if 'FAILURES' in line)
+    failures_end = next(index for index, line in enumerate(result.outlines) if 'short test summary' in line)
+    e_lines = [line.strip() for line in result.outlines[failures_start + 2 : failures_end]]
+    assert e_lines == [
+        'black failed:',
+        '--- before',
+        '+++ after',
+        '@@ -4 +4 @@',
+        '-x·=[1,2,·3]',
+        '+x·=·[1,·2,·3]',
+    ]
+
+
 def test_black_error_multiline(pytester: pytest.Pytester):
     pytester.makefile(
         '.md',