improving-frontend-coverage

name	improving-frontend-coverage
description	Runs frontend unit tests with coverage, analyzes coverage reports, and implements meaningful tests to increase coverage by ~0.2%. Use when you want to systematically improve frontend test coverage with high-value test cases.

Improving frontend coverage

Increase frontend unit test coverage by ~0.2% through meaningful tests that add real value.

Be fully autonomous — Do NOT stop or pause to ask for confirmation. Keep iterating (analyze → implement → verify) until the 0.2% coverage target is reached. If you encounter ambiguities about what to test, make a reasonable choice and proceed.

Workflow

Step 1: Run tests with coverage

COVERAGE_JSON=1 make frontend-tests  # ~5 min

Reports generated in frontend/coverage/:

• coverage-summary.json - Per-file percentages (lines, branches, functions)
• coverage-final.json - Line-level data with uncovered line numbers (hit count 0 in s, f, b maps)

Step 2: Analyze and prioritize

Read coverage-summary.json to find files with:

1. Large size + below-average coverage (high impact)
2. Core components in lib/src/components/
3. Utility functions in utils/src/

Skip: >97% coverage, auto-generated, .d.ts, test files.

Step 3: Implement tests (in subagent)

Launch a subagent to implement tests for each prioritized file. Provide the subagent with:

• The target file path and its uncovered lines from coverage-final.json
• Instructions to read the source, existing tests, and write new tests
• The test selection guidelines below

The subagent should:

1. Read source and existing tests to understand gaps
2. Write tests for: conditional rendering, event handlers, error states, edge cases, accessibility
3. Follow RTL best practices: query by role/label, test behavior not implementation
4. Run the new tests to verify they pass: cd frontend && yarn test path/to/Component.test.tsx

Step 4: Verify and iterate

cd frontend && yarn test path/to/Component.test.tsx  # Run new tests
COVERAGE_JSON=1 make frontend-tests                   # Measure progress

Repeat steps 2-4 until coverage improves by ≥0.2%, then run make check.

Step 5: Simplify, review, and address feedback

Once all tests pass and coverage target is met:

1. Run the simplifying-local-changes subagent to clean up and simplify the code changes. Wait for completion.
2. Run the reviewing-local-changes subagent to review the changes. Wait for completion and read the review output.
3. Address the review feedback: for each recommendation, implement it if valid and improves code quality; skip with brief reasoning if not applicable or would over-engineer.
4. Run /checking-changes to verify everything still passes after changes.

Test selection

DO test: Conditional rendering, user interactions, prop variations, error handling, accessibility, edge cases (null, empty, max values).

DON'T test: Pass-through props, styling, library internals, implementation details, already well-covered code.

Coverage exclusions: Use /* istanbul ignore next */ sparingly for code that genuinely doesn't need testing. Always include a reason (e.g., /* istanbul ignore next -- defensive */):

• Browser-specific branches that can't run in jsdom (/* istanbul ignore next -- browser-only */)
• Defensive fallbacks that should never execute (/* istanbul ignore next -- defensive */)
• Framework-required boilerplate (/* istanbul ignore next -- exhaustive */)

Notes

• Quality > coverage numbers - skip tests that don't catch real bugs
• Test files: co-located as <Component>.test.tsx
• Use /checking-changes after implementing tests