Add high-coverage tests for `analysis_utils.py`

[lamurian]

User Story

As a developer, I want src/python/analysis_utils.py to have automated tests covering at least 85% of its functionality, so that I can ensure correctness, prevent regressions, and maintain confidence in analysis utilities.

Description

analysis_utils.py contains functions for data processing and analysis. Currently, the module lacks sufficient automated test coverage. Implementing targeted tests will verify each function behaves as expected across normal, edge, and error scenarios. Coverage should reach at least 85% to comply with project quality standards.

Proposed Flow

• Review all functions in src/python/analysis_utils.py and identify testable behaviors
• Write unit tests for core functionality, including:
  • Normal input scenarios
  • Edge cases (empty arrays, missing values, unusual data types)
  • Error handling and invalid input
• Use a testing framework (e.g., pytest) and coverage tool
• Run coverage report and verify ≥85% coverage
• Refactor tests for clarity and maintainability
• Integrate tests into CI pipeline to enforce coverage threshold

Reference

• src/python/analysis_utils.py (source module to test)
• Existing test framework and coverage configuration at src/python/tests

Notes:

• Focus on testing return values, exceptions, and boundary conditions.
• Ensure reproducible results and deterministic behavior in tests.
• Include comments to indicate which functions are covered and any intentional gaps if certain lines cannot be reasonably tested.