Add Test Coverage

When adding test coverage to existing untested code:

1. Run the coverage tool to identify which functions and branches are uncovered.
2. Prioritize business-critical code and code with high change frequency.
3. Start by writing tests for the current behavior — even if you suspect bugs. Capture what the code does now.
4. Use the existing test patterns in the project. Don’t introduce a new testing style.
5. Focus on behavior, not lines. A test that verifies correct output for a given input is more valuable than one that merely executes code.
6. After adding tests, run mutation testing or break the code deliberately to verify your tests actually catch failures.