Add test for escaped negation pattern parsing

Test demonstrates the fix for escaped character handling order:
- Escaped negation patterns are treated as literals, not negations
- Real negation patterns properly override ignore rules

test/serena/util/test_file_system.py

@@ -419,6 +419,38 @@ build/
         assert "#not-a-comment.txt" in patterns
         assert "!not-negation.txt" in patterns
 
+    def test_escaped_negation_patterns(self):
+        test_dir = self.repo_path / "test_escaped_negation"
+        test_dir.mkdir()
+
+        gitignore = test_dir / ".gitignore"
+        gitignore.write_text(
+            """*.log
+\\!not-negation.log
+!actual-negation.log
+"""
+        )
+
+        parser = GitignoreParser(str(test_dir))
+        specs = parser.get_ignore_specs()
+
+        assert len(specs) == 1
+        patterns = specs[0].patterns
+
+        # Key assertions: escaped exclamation becomes literal, real negation preserved
+        assert "!not-negation.log" in patterns  # escaped -> literal
+        assert "!actual-negation.log" in patterns  # real negation preserved
+
+        # Test the actual behavioral difference between escaped and real negation:
+        # *.log pattern should ignore test.log
+        assert parser.should_ignore("test.log")
+
+        # Escaped negation file should still be ignored by *.log pattern
+        assert parser.should_ignore("!not-negation.log")
+
+        # Actual negation should override the *.log pattern
+        assert not parser.should_ignore("actual-negation.log")
+
     def test_glob_patterns(self):
         """Test various glob patterns work correctly."""
         test_dir = self.repo_path / "test_glob"