find-coverage-gaps

TODAY=!date +%Y-%m-%d

Coverage Gaps

Finds the parts of the codebase with the least test coverage, then ranks them by churn and complexity so the most important gaps surface first. Low coverage in a stable file is a minor concern; low coverage in a file that changes constantly and is hard to understand is a production risk.

Prerequisites

• Working directory is the root of the repository
• Optional: $1 — path to limit the scan (defaults to .)
• Tests must be runnable; coverage data is generated by running the test suite
• Language-specific tools:
  • Python: pytest-cov (uv add --dev pytest-cov)
  • JavaScript/TypeScript: jest --coverage or vitest --coverage
  • Go: go test -cover ./...
  • Rust: cargo tarpaulin (cargo install cargo-tarpaulin)

Coverage Thresholds

Files below threshold are ranked by a risk score: (1 - coverage) × churn_commits × complexity_score.

Steps

1. Run the Test Suite with Coverage

Python:

python -m pytest ${1:-.} --cov=${1:-.} --cov-report=term-missing --cov-report=json:coverage.json -q 2>&1 | tail -40

JavaScript/TypeScript — Jest:

npx jest --coverage --coverageReporters=json-summary --coverageDirectory=.coverage 2>/dev/null
cat .coverage/coverage-summary.json | jq '.[] | select(.lines.pct < 80) | {file: ., pct: .lines.pct}' 2>/dev/null | head -40

JavaScript/TypeScript — Vitest:

npx vitest run --coverage 2>/dev/null

Go:

go test -coverprofile=coverage.out ./... 2>/dev/null && go tool cover -func=coverage.out | rg -v "100.0%" | sort -k3 -n | head -30

Rust:

cargo tarpaulin --out Json --output-dir .coverage 2>/dev/null

2. Parse Coverage Results

Extract per-file coverage percentages from the generated report:

Python — from coverage.json:

python3 -c "
import json, sys
data = json.load(open('coverage.json'))
files = [(v['summary']['percent_covered'], k) for k, v in data['files'].items()]
for pct, f in sorted(files):
    if pct < 80:
        print(f'{pct:5.1f}%  {f}')
" 2>/dev/null