diff-coverage

name	diff-coverage
description	Verify 100% diff line AND branch coverage vs trunk after code changes. Runs vitest coverage, then diff-cover (line) + diff-branch-cov.py (branch). Both required. Use after any src/**/*.{ts,tsx} or api/**/*.ts edit before handing work back.

Diff coverage workflow

Hard rule: after every code change on a branch, both line-diff and branch-diff coverage vs trunk must be 100%. Add or extend tests until clean before handing work back.

Steps

1. bun run test:coverage — runs vitest with v8 coverage, writes coverage/lcov.info (configured in vitest.config.ts).
2. /tmp/dc-venv/bin/diff-cover coverage/lcov.info --compare-branch=trunk — % changed lines covered + missing line numbers per file.
   • diff-cover lives in local venv at /tmp/dc-venv. If gone, recreate: python3 -m venv /tmp/dc-venv && /tmp/dc-venv/bin/pip install diff-cover.
3. python3 scripts/diff-branch-cov.py trunk — partial/untaken branches on changed lines (e.g. L16: 1/2 taken). Exits non-zero if any found. Reproduces Codecov's branch view locally; lcov marks a line "hit" even if only one branch arm ran, so this catches what diff-cover misses.
4. For each file under Missing lines (step 2) or partial branches (step 3): read those lines, add a test exercising them, re-run all three commands. Repeat until step 2 reads Coverage: 100% AND step 3 exits 0.

Notes

• Coverage scope set in vitest.config.ts (include: src/**/*.{ts,tsx}, api/**/*.ts). Files outside scope don't count even if changed.
• Heavy browser-only deps (e.g. html2canvas) should be mocked with vi.mock(...) not skipped — see src/__tests__/screenshotCapture.test.ts for the pattern.
• Step 3 base branch is configurable (trunk, staging, etc.) — match whatever the PR will target.