9f48f7afeb
Added 3 new tests for missing error paths: - Invalid en passant square parsing (e.g., "x5") - Half-move clock non-integer (e.g., "abc") - Full-move number non-integer (e.g., "abc") Updated 3 existing error tests to verify error messages: - "expected 6" for invalid parts count - "color" for invalid active color - "castling" for invalid castling rights All error assertions now use .fold() to verify message content, improving test robustness. Test count increased from 19 to 22. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>