Format Handler Tests (`tests/formats/test_quickbook.py`)

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Problem

The QuickBook format handler (item 2) must be validated against Weblate's format contract. Tests must verify round-trip fidelity, monolingual behavior, extension autodetection, and correct interaction with the Weblate translation unit API. Without these tests, format handler bugs could silently corrupt translations.

Acceptance Criteria

• tests/formats/test_quickbook.py exists with pytest-style test functions
• Round-trip test: load a .qbk fixture file via QuickBookFormat.load(), then save() — output matches input byte-for-byte
• Monolingual contract test: verify QuickBookFormat.monolingual is True and that load() produces units with source populated and target empty
• autodetect_extensions test: verify (".qbk",) is returned
• format_id test: verify the format returns "quickbook"
• name test: verify human-readable name is returned
• Edge case: load a file with code blocks and verify they are not split into translatable units
• Edge case: load a file with tables and verify cell content is extracted as separate units
• Test fixtures are stored in tests/fixtures/ as .qbk files

Implementation Notes

• Create at least 3 fixture files: a minimal single-section file, a complex file with tables/code/images, and an empty file.
• If Weblate's test infrastructure provides a BaseFormatTest mixin, consider subclassing it for contract conformance.
• These tests validate the format handler's Weblate integration; William's tests/utils/test_quickbook.py (item 9) validates the underlying parser independently.
• Use pytest-tmp-files or tmp_path fixture for any write-back tests.

References

• Related files: tests/formats/test_quickbook.py, tests/fixtures/*.qbk, src/boost_weblate/formats/quickbook.py
• Upstream: weblate/formats/tests/test_txt.py for test patterns