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>
Janis
9f48f7afeb