Feature Description

Set up a multi-layered testing strategy for validating new python-docx features (starting with comments support). The approach ensures correctness without requiring Microsoft Word for every test run, while still producing files that Word will accept.

Testing Layers

Layer 1: XML Structure Tests (every PR)

• Validate that python-docx produces the correct OOXML elements
• For comments: assert word/comments.xml contains w:comment elements with correct attributes (w:id, w:author, w:date, w:initials)
• Assert word/document.xml contains matching w:commentRangeStart and w:commentRangeEnd markers
• Assert [Content_Types].xml includes the comments content type
• Assert word/_rels/document.xml.rels includes the comments relationship
• Follow existing test patterns in the codebase (unit tests with pytest)

Layer 2: OOXML Schema Validation (every PR)

• Validate output XML against the official ECMA-376 OOXML XSD schemas
• Use lxml.etree.XMLSchema for validation
• Create a pytest fixture or helper that validates a generated .docx against the schemas
• Schemas are publicly available from ECMA — download and include in test fixtures or fetch during CI setup
• Catches: missing required elements, invalid attributes, wrong element ordering

Layer 3: Round-Trip Tests (every PR)

• Write a feature with python-docx → save → re-open with python-docx → assert data reads back correctly
• For comments:
  • Create document with comments → re-read → assert comment text, author, date match
  • Create threaded comments → re-read → assert reply threading is preserved
  • Create comments on specific text ranges → re-read → assert ranges are correct
  • Modify comments → save → re-read → assert modifications persisted
  • Delete comments → save → re-read → assert comments removed

Layer 4: Reference File Comparison (every PR)

• Maintain a set of reference .docx files created in Microsoft Word (one-time manual step)
• For comments: create a Word doc with various comment scenarios:
  • Simple comment on a word
  • Comment on a paragraph
  • Threaded reply chain (2-3 levels)
  • Comment by multiple authors
  • Comment with formatted text (bold, italic)
• Test fixtures read these reference files and assert python-docx parses them correctly
• Optionally compare XML output of python-docx against reference file XML for structural equivalence
• Store reference files in tests/fixtures/ or tests/ref-docs/

Layer 5: LibreOffice Headless Validation (CI, optional)

• Install LibreOffice in CI (sudo apt-get install libreoffice-writer)
• After generating a .docx, convert to PDF headlessly:

  libreoffice --headless --convert-to pdf output.docx

• If LibreOffice rejects the file or errors during conversion, the test fails
• Optionally: render to images and do pixel-based visual regression testing for critical features
• Add as a separate CI job or test marker so it doesn't slow down the main test suite

Implementation

New test helpers (tests/helpers/)

• validate_ooxml(docx_path) — unzips and validates all XML parts against OOXML schemas
• extract_xml_part(docx_path, part_name) — extracts a specific XML part for assertion
• assert_round_trip(create_fn, assert_fn) — creates a doc, saves, re-opens, runs assertions

CI changes

• Add lxml to dev dependencies if not already present (for schema validation)
• Optionally add a LibreOffice validation job in GitHub Actions

Reference file creation (one-time manual)

• Create reference .docx files in Microsoft Word for each feature area
• Document what each reference file contains in a tests/ref-docs/README.md
• Commit to the repo as test fixtures

Acceptance Criteria

• XML structure test helpers created and documented
• OOXML schema validation helper created (with schema files or download script)
• Round-trip test pattern established with at least one example test
• Reference file comparison pattern established
• LibreOffice headless validation working in CI (can be a separate optional job)
• All test helpers are usable for the upcoming comments feature

Dependencies

None — this should be implemented before or alongside the comments feature.

Out of Scope

• The comments feature itself (separate issue)
• Visual regression testing with screenshot comparison (future enhancement)
• Testing with actual Microsoft Word (manual only, not in CI)