Coverage Check

Context

Run in parallel:

• git diff --name-only - get unstaged files
• git diff -U0 --no-color - get changed line numbers

Commands

Sequential:

1. npm run test:ci - vitest with coverage
2. npm run coverage:report - generate lcov/text reports

Workflow

1. Get unstaged files and line ranges (parallel):
   • git diff --name-only
   • git diff -U0 --no-color
2. Run coverage:
   • npm run test:ci
   • npm run coverage:report
3. Save diff to a temp file, then run:

   git diff -U0 --no-color > /tmp/changes.diff
   python3 scripts/parse-lcov.py --lcov coverage/lcov.info --diff /tmp/changes.diff
   

4. Report uncovered lines from stdout: file.ts:42
5. Summary from stderr: X/Y changed lines covered

LCOV Format

Parse coverage/lcov.info:

SF:src/utils/helper.ts
DA:10,1    # line 10, covered (hit 1 time)
DA:11,0    # line 11, NOT covered
DA:12,5    # line 12, covered (hit 5 times)
end_of_record

Key fields:

• SF: -- source file path
• DA:line,hits -- 0 = uncovered, >0 = covered
• end_of_record -- end of file section

Match SF: paths to git diff files. For each changed line, check DA: entry. If hits is 0, report as uncovered.

Anti-Rationalization

Excuse	Rebuttal
"Coverage doesn't guarantee quality"	True, but uncovered code guarantees zero automated verification.
"It's just a config change"	Config changes break production too. If there's logic, check coverage.
"100% is overkill"	Nobody asked for 100%. Check that changed lines are covered.
"The test suite is already green"	Green suite with uncovered changes = false confidence.

Rules

• Only analyze unstaged changes (git diff)
• Use sequential commands: test:ci then coverage:report
• Use scripts/parse-lcov.py to parse lcov data and map to changed lines
• Report uncovered lines: file.ts:42
• Ignore files without coverage data (non-code files)

Error Handling

• npm run test:ci fails -- report test failures and stop
• coverage/lcov.info not found -- verify coverage.reporter includes lcov in test runner config
• git diff returns no changes -- report no unstaged changes to check