/vitest

Code Coverage

Setup

# Run tests with coverage
vitest run --coverage

Configuration

// vitest.config.ts
defineConfig({
  test: {
    coverage: {
      // Provider: 'v8' (default, faster) or 'istanbul' (more compatible)
      provider: 'v8',
      
      // Enable coverage
      enabled: true,
      
      // Reporters
      reporter: ['text', 'json', 'html'],
      
      // v4: define `include` to report uncovered files too.
      // Without it, only files loaded during the run are reported.
      include: ['src/**/*.{ts,tsx}'],
      
      // Exclusion is applied to files matched by `include`
      exclude: [
        '**/*.d.ts',
        '**/*.test.ts',
      ],
      
      // Thresholds
      thresholds: {
        lines: 80,
        functions: 80,
        branches: 80,
        statements: 80,
      },

      // v5 (v8 only): also cover node:child_process / node:worker_threads
      // spawned during the run (adds overhead via NODE_V8_COVERAGE)
      autoAttachSubprocess: false,
    },
  },
})

Providers

V8 (Default)

npm i -D @vitest/coverage-v8

• Faster, no pre-instrumentation
• Uses V8's native coverage
• v4 uses AST-based remapping (as accurate as Istanbul); expect coverage numbers to shift when upgrading from v3
• Recommended for most projects

Istanbul

npm i -D @vitest/coverage-istanbul

• Pre-instruments code
• Works in any JS runtime
• More overhead but widely compatible

Reporters

coverage: {
  reporter: [
    'text',           // Terminal output
    'text-summary',   // Summary only
    'json',           // JSON file
    'html',           // HTML report
    'lcov',           // For CI tools
    'cobertura',      // XML format
  ],
  reportsDirectory: './coverage',
}

Thresholds

Fail tests if coverage is below threshold:

coverage: {
  thresholds: {
    // Global thresholds
    lines: 80,
    functions: 75,
    branches: 70,
    statements: 80,
    
    // Per-file thresholds
    perFile: true,
    
    // Auto-update thresholds (for gradual improvement)
    // v5: a function receives (newThreshold, previousThreshold)
    autoUpdate: true,

    // v5: glob thresholds no longer inherit top-level `perFile` — set it per glob
    'src/utils/**': { lines: 80, perFile: true },
  },
}

Ignoring Code

V8

/* v8 ignore next -- @preserve */
function ignored() {
  return 'not covered'
}

/* v8 ignore start -- @preserve */
// All code here ignored
/* v8 ignore stop -- @preserve */

Istanbul

/* istanbul ignore next -- @preserve */
function ignored() {}

/* istanbul ignore if -- @preserve */
if (condition) {
  // ignored
}

Note: @preserve keeps comments through esbuild.

Package.json Scripts

{
  "scripts": {
    "test": "vitest",
    "test:coverage": "vitest run --coverage",
    "test:coverage:watch": "vitest --coverage"
  }
}

Vitest UI Coverage

Enable HTML coverage in Vitest UI:

coverage: {
  enabled: true,
  reporter: ['text', 'html'],
}

Run with vitest --ui to view coverage visually.

CI Integration

# GitHub Actions
- name: Run tests with coverage
  run: npm run test:coverage

- name: Upload coverage to Codecov
  uses: codecov/codecov-action@v3
  with:
    files: ./coverage/lcov.info

Coverage with Sharding

Merge coverage from sharded runs (blobs default to .vitest/blob/):

vitest run --shard=1/3 --coverage --reporter=blob
vitest run --shard=2/3 --coverage --reporter=blob
vitest run --shard=3/3 --coverage --reporter=blob

vitest --merge-reports --coverage --reporter=json

v5 Changes

• include/exclude match relative paths (not absolute-with-contains), so patterns catch fewer files than v4 — a wildcard-free pattern like 'src' means src/**. Re-verify the reported file set after upgrading.
• Glob thresholds don't inherit top-level perFile — set perFile on each glob that needs it.
• coverage.autoAttachSubprocess (v8) tracks child-process/worker-thread coverage.
• Istanbul moved to the maintained @vitest/istanbuljs fork; the v8 provider merges reports with bounded memory.

v4 Changes

• coverage.all and coverage.extensions removed — only covered files are reported unless coverage.include is set.
• coverage.ignoreEmptyLines removed; lines without runtime code are no longer counted.
• coverage.experimentalAstAwareRemapping removed — AST remapping is the default and only mode for V8.
• Programmatic coverage APIs moved from vitest/coverage to vitest/node.

Key Points

• V8 is faster, Istanbul is more compatible
• Use --coverage flag or coverage.enabled: true
• Define coverage.include to report uncovered source files
• Set thresholds to enforce minimum coverage
• Use @preserve comment to keep ignore hints (e.g. /* v8 ignore next -- @preserve */)