**Purpose**: Test FilenameExtractor edge cases and new documentation.

**Key Test Areas**:
- Parameter handling (null, empty, missing)
- Special character handling
- Input stream validation (not consumption)
- Edge cases (long filenames, paths, whitespace)

**Test Count**: 10 tests

**Key Scenarios**:
- ✅ Valid filename extraction
- ✅ Null parameters handling
- ✅ Empty/missing resource name