Coverage

Vitest supports Native code coverage via v8 and instrumented code coverage via istanbul.

Coverage Providers

Both v8 and istanbul support are optional. By default, v8 will be used.

You can select the coverage tool by setting test.coverage.provider to v8 or istanbul:

vitest.config.ts

import { defineConfig } from 'vitest/config'

export default defineConfig({
  test: {
    coverage: {
      provider: 'istanbul' // or 'v8'
    },
  },
})

When you start the Vitest process, it will prompt you to install the corresponding support package automatically.

Or if you prefer to install them manually:

v8

npm i -D @vitest/coverage-v8

istanbul

npm i -D @vitest/coverage-istanbul

Coverage Setup

TIP

It's recommended to always define coverage.include in your configuration file. This helps Vitest to reduce the amount of files picked by coverage.all.

To test with coverage enabled, you can pass the --coverage flag in CLI. By default, reporter ['text', 'html', 'clover', 'json'] will be used.

package.json

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

To configure it, set test.coverage options in your config file:

vitest.config.ts

import { defineConfig } from 'vitest/config'

export default defineConfig({
  test: {
    coverage: {
      reporter: ['text', 'json', 'html'],
    },
  },
})

Custom Coverage Reporter

You can use custom coverage reporters by passing either the name of the package or absolute path in test.coverage.reporter:

vitest.config.ts

import { defineConfig } from 'vitest/config'

export default defineConfig({
  test: {
    coverage: {
      reporter: [
        // Specify reporter using name of the NPM package
        ['@vitest/custom-coverage-reporter', { someOption: true }],

        // Specify reporter using local path
        '/absolute/path/to/custom-reporter.cjs',
      ],
    },
  },
})

Custom reporters are loaded by Istanbul and must match its reporter interface. See built-in reporters' implementation for reference.

custom-reporter.cjs

const { ReportBase } = require('istanbul-lib-report')

module.exports = class CustomReporter extends ReportBase {
  constructor(opts) {
    super()

    // Options passed from configuration are available here
    this.file = opts.file
  }

  onStart(root, context) {
    this.contentWriter = context.writer.writeFile(this.file)
    this.contentWriter.println('Start of custom coverage report')
  }

  onEnd() {
    this.contentWriter.println('End of custom coverage report')
    this.contentWriter.close()
  }
}

Custom Coverage Provider

It's also possible to provide your custom coverage provider by passing 'custom' in test.coverage.provider:

vitest.config.ts

import { defineConfig } from 'vitest/config'

export default defineConfig({
  test: {
    coverage: {
      provider: 'custom',
      customProviderModule: 'my-custom-coverage-provider'
    },
  },
})

The custom providers require a customProviderModule option which is a module name or path where to load the CoverageProviderModule from. It must export an object that implements CoverageProviderModule as default export:

my-custom-coverage-provider.ts

import type {
  CoverageProvider,
  CoverageProviderModule,
  ResolvedCoverageOptions,
  Vitest
} from 'vitest'

const CustomCoverageProviderModule: CoverageProviderModule = {
  getProvider(): CoverageProvider {
    return new CustomCoverageProvider()
  },

  // Implements rest of the CoverageProviderModule ...
}

class CustomCoverageProvider implements CoverageProvider {
  name = 'custom-coverage-provider'
  options!: ResolvedCoverageOptions

  initialize(ctx: Vitest) {
    this.options = ctx.config.coverage
  }

  // Implements rest of the CoverageProvider ...
}

export default CustomCoverageProviderModule

Please refer to the type definition for more details.

Changing the Default Coverage Folder Location

When running a coverage report, a coverage folder is created in the root directory of your project. If you want to move it to a different directory, use the test.coverage.reportsDirectory property in the vitest.config.js file.

vitest.config.js

import { defineConfig } from 'vite'

export default defineConfig({
  test: {
    coverage: {
      reportsDirectory: './tests/unit/coverage'
    }
  }
})

Ignoring Code

Both coverage providers have their own ways how to ignore code from coverage reports:

• v8
• ìstanbul

When using TypeScript the source codes are transpiled using esbuild, which strips all comments from the source codes (esbuild#516). Comments which are considered as legal comments are preserved.

For istanbul provider you can include a @preserve keyword in the ignore hint. Beware that these ignore hints may now be included in final production build as well.

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

For v8 this does not cause any issues. You can use v8 ignore comments with Typescript as usual:

/* v8 ignore next 3 */
if (condition) {

Other Options

To see all configurable options for coverage, see the coverage Config Reference.

Coverage performance

If code coverage generation is slow on your project, see Profiling Test Performance | Code coverage.

Vitest UI

You can check your coverage report in Vitest UI.

Vitest UI will enable coverage report when it is enabled explicitly and the html coverage reporter is present, otherwise it will not be available:

• enable coverage.enabled=true in your configuration file or run Vitest with --coverage.enabled=true flag
• add html to the coverage.reporter list: you can also enable subdir option to put coverage report in a subdirectory