Write and read-back verification
After writing the target keyword, the output file is parsed again. A result is treated as successful only when dc:subject contains the exact contains-synthetic-performer value.
Pixel payload preservation
For JPEG, tests compare the compressed scan data before and after tagging. For PNG, tests compare the IDAT payload. The image dimensions are also checked. This verifies that the metadata operation did not decode and re-encode the visible image.
Metadata and file-state coverage
Tests confirm that an existing target keyword is not duplicated and unrelated XMP keywords remain present. RGB, CMYK, low DPI, missing DPI, large files, indexed PNG, and animated PNG states are represented as lightweight status labels when the file can still be tagged.
Blocking behavior
Unsupported formats, corrupt image containers, and XMP packets that cannot be modified safely produce a file-level error. Batch processing can continue for other files, and ZIP output includes only verified results.