test_schemaview.py - add comprehensive tests for class relationships

[ialarmedalien]

As the title suggests, adds comprehensive tests for class_* relationships:

• class_children
• class_parents
• class_ancestors
• class_descendants
• class_roots
• class_leaves

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.48%. Comparing base (878d01e) to head (cfd5f90).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #466   +/-   ##
=======================================
  Coverage   77.48%   77.48%           
=======================================
  Files          52       52           
  Lines        4464     4464           
  Branches      970      970           
=======================================
  Hits         3459     3459           
  Misses        781      781           
  Partials      224      224           

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