Expand Unit Tests

Expand existing unit tests adapted to project’s testing framework:

1. Analyze coverage: Run coverage report to identify untested branches, edge cases, and low-coverage areas
2. Identify gaps: Review code for logical branches, error paths, boundary conditions, null/empty inputs
3. Write tests using project’s framework:
   • Jest/Vitest/Mocha (JavaScript/TypeScript)
   • pytest/unittest (Python)
   • Go testing/testify (Go)
   • Rust test framework (Rust)
4. Target specific scenarios:
   • Error handling and exceptions
   • Boundary values (min/max, empty, null)
   • Edge cases and corner cases
   • State transitions and side effects
5. Verify improvement: Run coverage again, confirm measurable increase

Present new test code blocks only. Follow existing test patterns and naming conventions.