Pull Request Title: Update code formatting to use ruff format instead of black

pytest_examples/eval_example.py

@@ -8,7 +8,7 @@
 from _pytest.outcomes import Failed as PytestFailed
 
 from .config import DEFAULT_LINE_LENGTH, ExamplesConfig
-from .lint import FormatError, black_check, black_format, ruff_check, ruff_format
+from .lint import FormatError, ruff_check, ruff_format
 from .run_code import InsertPrintStatements, run_code
 
 if TYPE_CHECKING:
@@ -182,20 +182,8 @@ def lint(self, example: CodeExample) -> None:
         Args:
             example: The example to lint.
         """
-        self.lint_black(example)
         self.lint_ruff(example)
 
-    def lint_black(self, example: CodeExample) -> None:
-        """Lint the example using black.
-
-        Args:
-            example: The example to lint.
-        """
-        example.test_id = self._test_id
-        try:
-            black_check(example, self.config)
-        except FormatError as exc:
-            raise PytestFailed(str(exc), pytrace=False) from None
 
     def lint_ruff(
         self,
@@ -219,20 +207,6 @@ def format(self, example: CodeExample) -> None:
             example: The example to format.
         """
         self.format_ruff(example)
-        self.format_black(example)
-
-    def format_black(self, example: CodeExample) -> None:
-        """Format the example using black, requires `--update-examples`.
-
-        Args:
-            example: The example to lint.
-        """
-        self._check_update(example)
-
-        new_content = black_format(example.source, self.config, remove_double_blank=example.in_py_file())
-        if new_content != example.source:
-            example.source = new_content
-            self._mark_for_update(example)
 
     def format_ruff(
         self,

pytest_examples/lint.py

@@ -1,20 +1,19 @@
 from __future__ import annotations as _annotations
 
 import re
+import difflib
 from subprocess import PIPE, Popen
 from textwrap import indent
 from typing import TYPE_CHECKING
 
-from black import format_str as black_format_str
-from black.output import diff as black_diff
 from ruff.__main__ import find_ruff_bin
 
 from .config import ExamplesConfig
 
 if TYPE_CHECKING:
     from .find_examples import CodeExample
 
-__all__ = 'ruff_check', 'ruff_format', 'black_check', 'black_format', 'code_diff', 'FormatError'
+__all__ = 'ruff_check', 'ruff_format', 'code_diff', 'FormatError'
 
 
 class FormatError(ValueError):
@@ -67,28 +66,12 @@ def replace_offset(m: re.Match):
         return stdout
 
 
-def black_format(source: str, config: ExamplesConfig, *, remove_double_blank: bool = False) -> str:
-    # hack to avoid black complaining about our print output format
-    before_black = re.sub(r'^( *#)> ', r'\1 > ', source, flags=re.M)
-    after_black = black_format_str(before_black, mode=config.black_mode())
-    # then revert it back
-    after_black = re.sub(r'^( *#) > ', r'\1> ', after_black, flags=re.M)
-    if remove_double_blank:
-        after_black = re.sub(r'\n{3}', '\n\n', after_black)
-    return after_black
-
-
-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, config)
-        raise FormatError(f'black failed:\n{indent(diff, "  ")}')
 
 
 def code_diff(example: CodeExample, after: str, config: ExamplesConfig) -> str:
-    diff = black_diff(sub_space(example.source, config), sub_space(after, config), 'before', 'after')
-
-    def replace_at_line(match: re.Match) -> str:
+    before_lines = sub_space(example.source, config).splitlines(keepends=True)
+    after_lines = sub_space(after, config).splitlines(keepends=True)
+    diff = ''.join(difflib.unified_diff(before_lines, after_lines, 'before', 'after'))
         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)}'