Add comprehensive tests for Groups API (24 tests)
Tests include:
- Group model validation (8 tests)
- Group, GroupCreate, GroupUpdate models
- Field validation, name validation
- Minimal and full field tests
- Sync GroupsEndpoint (8 tests)
- List, get, create, update, delete operations
- User assignment/unassignment operations
- Validation error handling
- Async AsyncGroupsEndpoint (8 tests)
- Complete async coverage matching sync API
- All CRUD operations tested
- User management operations
All 24 tests passing. Achieves comprehensive coverage for Groups API.
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Co-Authored-By: Claude <noreply@anthropic.com>
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