/radar

Coverage Strategy

Purpose: Choose the right coverage signal, enforce safe thresholds, and separate real risk from vanity metrics. Read this when Radar runs in AUDIT mode or when a team wants stronger coverage gates.

Contents:

• coverage type selection
• code-type thresholds
• diff coverage and ratchets
• dead code triage
• anti-patterns

Coverage Types Decision Matrix

Recommended Metrics By Code Type

Judge Integration

If coverage must feed Judge's UQS, keep the composite weighting intact:

radar_score = (line × 0.4) + (branch × 0.4) + (function × 0.2)

That weighting makes branch improvements the highest-leverage change when line coverage is already acceptable.

Diff Coverage

Use diff coverage to stop new code from lowering quality.

pip install diff-cover
npx vitest run --coverage
diff-cover coverage/lcov.info --compare-branch=main --fail-under=80

Default rule:

• new or changed lines should stay at 80%+
• do not accept lower diff coverage just because global coverage is high

Framework Coverage Config

Vitest

export default defineConfig({
  test: {
    coverage: {
      provider: 'v8',
      reporter: ['text', 'lcov', 'json-summary'],
      thresholds: {
        lines: 80,
        branches: 80,
        functions: 75,
        statements: 80,
      },
    },
  },
});

Jest

module.exports = {
  coverageDirectory: 'coverage',
  coverageReporters: ['text', 'lcov', 'json-summary'],
  coverageThreshold: {
    global: {
      lines: 80,
      branches: 80,
      functions: 75,
      statements: 80,
    },
  },
};

pytest / Go / Java

pytest --cov=src --cov-report=term-missing --cov-report=lcov:coverage/lcov.info
go test ./... -coverprofile=coverage.out -covermode=atomic
go tool cover -func=coverage.out

Use JaCoCo bundle rules with 0.80 line coverage as the default floor unless the repo already uses a stricter gate.

Coverage Ratchet Strategy

Ratchet upward instead of chasing an arbitrary global number.

Rules

• PR coverage must be >= the default branch coverage
• changed modules should not regress below their current baseline
• weak modules should improve incrementally, not be exempt forever

Per-Module Example

Dead Code vs Untested Code

Do not raise coverage by testing code that should be deleted.

Multi-Module Coverage

Useful patterns:

• merge lcov.info files for monorepos
• use Codecov flags per package
• keep one combined HTML report for local triage

Example:

npx lcov-result-merger 'packages/*/coverage/lcov.info' merged.lcov
genhtml merged.lcov --output-directory combined-coverage

Anti-Patterns

Quick Reference