1---
2name: code-coverage
3description: Code coverage with V8 or Istanbul providers
4---
5 
6# Code Coverage
7 
8## Setup
9 
10```bash
11# Run tests with coverage
12vitest run --coverage
13```
14 
15## Configuration
16 
17```ts
18// vitest.config.ts
19defineConfig({
20  test: {
21    coverage: {
22      // Provider: 'v8' (default, faster) or 'istanbul' (more compatible)
23      provider: 'v8',
24      
25      // Enable coverage
26      enabled: true,
27      
28      // Reporters
29      reporter: ['text', 'json', 'html'],
30      
31      // Files to include
32      include: ['src/**/*.{ts,tsx}'],
33      
34      // Files to exclude
35      exclude: [
36        'node_modules/',
37        'tests/',
38        '**/*.d.ts',
39        '**/*.test.ts',
40      ],
41      
42      // Report uncovered files
43      all: true,
44      
45      // Thresholds
46      thresholds: {
47        lines: 80,
48        functions: 80,
49        branches: 80,
50        statements: 80,
51      },
52    },
53  },
54})
55```
56 
57## Providers
58 
59### V8 (Default)
60 
61```bash
62npm i -D @vitest/coverage-v8
63```
64 
65- Faster, no pre-instrumentation
66- Uses V8's native coverage
67- Recommended for most projects
68 
69### Istanbul
70 
71```bash
72npm i -D @vitest/coverage-istanbul
73```
74 
75- Pre-instruments code
76- Works in any JS runtime
77- More overhead but widely compatible
78 
79## Reporters
80 
81```ts
82coverage: {
83  reporter: [
84    'text',           // Terminal output
85    'text-summary',   // Summary only
86    'json',           // JSON file
87    'html',           // HTML report
88    'lcov',           // For CI tools
89    'cobertura',      // XML format
90  ],
91  reportsDirectory: './coverage',
92}
93```
94 
95## Thresholds
96 
97Fail tests if coverage is below threshold:
98 
99```ts
100coverage: {
101  thresholds: {
102    // Global thresholds
103    lines: 80,
104    functions: 75,
105    branches: 70,
106    statements: 80,
107    
108    // Per-file thresholds
109    perFile: true,
110    
111    // Auto-update thresholds (for gradual improvement)
112    autoUpdate: true,
113  },
114}
115```
116 
117## Ignoring Code
118 
119### V8
120 
121```ts
122/* v8 ignore next -- @preserve */
123function ignored() {
124  return 'not covered'
125}
126 
127/* v8 ignore start -- @preserve */
128// All code here ignored
129/* v8 ignore stop -- @preserve */
130```
131 
132### Istanbul
133 
134```ts
135/* istanbul ignore next -- @preserve */
136function ignored() {}
137 
138/* istanbul ignore if -- @preserve */
139if (condition) {
140  // ignored
141}
142```
143 
144Note: `@preserve` keeps comments through esbuild.
145 
146## Package.json Scripts
147 
148```json
149{
150  "scripts": {
151    "test": "vitest",
152    "test:coverage": "vitest run --coverage",
153    "test:coverage:watch": "vitest --coverage"
154  }
155}
156```
157 
158## Vitest UI Coverage
159 
160Enable HTML coverage in Vitest UI:
161 
162```ts
163coverage: {
164  enabled: true,
165  reporter: ['text', 'html'],
166}
167```
168 
169Run with `vitest --ui` to view coverage visually.
170 
171## CI Integration
172 
173```yaml
174# GitHub Actions
175- name: Run tests with coverage
176  run: npm run test:coverage
177 
178- name: Upload coverage to Codecov
179  uses: codecov/codecov-action@v3
180  with:
181    files: ./coverage/lcov.info
182```
183 
184## Coverage with Sharding
185 
186Merge coverage from sharded runs:
187 
188```bash
189vitest run --shard=1/3 --coverage --reporter=blob
190vitest run --shard=2/3 --coverage --reporter=blob
191vitest run --shard=3/3 --coverage --reporter=blob
192 
193vitest --merge-reports --coverage --reporter=json
194```
195 
196## Key Points
197 
198- V8 is faster, Istanbul is more compatible
199- Use `--coverage` flag or `coverage.enabled: true`
200- Include `all: true` to see uncovered files
201- Set thresholds to enforce minimum coverage
202- Use `@preserve` comment to keep ignore hints
203 
204<!-- 
205Source references:
206- https://vitest.dev/guide/coverage.html
207-->
208