feat: add social_preview check for Open Graph meta tags

Hanrequested to merge
duo/feature/2-social-preview-check into main

Plan

Add a new social_preview check to detect Open Graph meta tags (og:title and og:image) that enable rich link previews when shared on social networks and messaging apps.

Changes

  • Added social_preview check class in app/checks.py with pass/warn/fail logic:
    • Pass: Both og:title and og:image tags present
    • Warn: Only one of the two tags present
    • Fail: Neither tag present
  • Registered the check in CHECK_DEFINITIONS with 0.5 weight (small weight as specified)
  • Added comprehensive test cases in app/tests/test_checks.py:
    • Test for pass scenario (both tags present)
    • Test for warn scenarios (only title or only image)
    • Test for fail scenario (no tags)
    • Test for case-insensitive property matching
    • Test for empty content handling
  • Updated GOOD_HTML test fixture to include og:title and og:image for consistent test results
  • Integrated check into evaluate_page() function to run on all page evaluations

Test evidence

$ ruff check . && ruff format --check . && pytest -q
All checks passed!
29 files already formatted
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All tests pass including:

  • Unit tests for all three states (pass, warn, fail)
  • Integration tests verifying the check appears in evaluate_page results
  • API tests confirming the check is included in reports and score calculation
  • Code quality checks (ruff) pass without issues

Closes #2 (closed)

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