Create shared test utilities to reduce test code duplication

[ali90h]

Description

Extract common test setup, teardown, and utility patterns into shared test helper functions to reduce duplication and improve test maintainability.

Current Issues

• Duplicated test setup code across multiple test files
• Similar assertion patterns repeated in many tests
• Temporary file/directory creation patterns repeated
• Mock setup patterns duplicated

Proposed Solution

• Create tests/utils/ package with shared utilities:
  • test_fixtures.py for common test data and setup
  • test_helpers.py for assertion and utility functions
  • temp_utils.py for temporary file/directory management
  • mock_utils.py for common mocking patterns
• Refactor existing tests to use shared utilities

Acceptance Criteria

• Shared utilities cover common test patterns
• Test code duplication reduced by at least 30%
• All existing tests continue to pass
• New utilities are well-documented and tested
• Test execution time not negatively impacted