#coverage

• Type:

type CoverageOptions = {
  enabled?: boolean;
  provider?: 'istanbul' | 'v8';
  include?: string[];
  changed?: boolean | string;
  exclude?: string[];
  reporters?: CoverageReporter[];
  reportsDirectory?: string;
  reportOnFailure?: boolean;
  clean?: boolean;
  allowExternal?: boolean;
  thresholds?: CoverageThresholds;
};

type CoverageReporter = string | [string, Record<string, unknown>] | ReportBase;

• Default: undefined

Collect code coverage and generate coverage reports.

$ npx rstest --coverage

----------|---------|----------|---------|---------|-------------------
File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
----------|---------|----------|---------|---------|-------------------
All files |     100 |      100 |     100 |     100 |
 index.ts |     100 |      100 |     100 |     100 |
----------|---------|----------|---------|---------|-------------------

#Options

#enabled

• Type: boolean
• Default: false
• CLI: --coverage, --coverage=false, --no-coverage

Enable or disable test coverage collection.

npx rstest --coverage

import { defineConfig } from '@rstest/core';

export default defineConfig({
  coverage: {
    enabled: true,
  },
});

#provider

• Type: 'istanbul' | 'v8'
• Default: 'istanbul'
• CLI: --coverage.provider <provider>

The coverage provider to use. Rstest supports both istanbul and v8. Choose istanbul when you want SWC-based instrumentation performance and stable Istanbul semantics. Choose v8 when coverage is mainly limited by memory pressure; it usually has lower runtime memory usage because it does not inject coverage counters into every executed module.

import { defineConfig } from '@rstest/core';

export default defineConfig({
  coverage: {
    enabled: true,
    provider: 'v8',
  },
});

#Istanbul provider

Istanbul is a widely used JavaScript code coverage tool that collects coverage through instrumentation.

To enable istanbul coverage, install @rstest/coverage-istanbul first.

npm add @rstest/coverage-istanbul -D

yarn add @rstest/coverage-istanbul -D

pnpm add @rstest/coverage-istanbul -D

bun add @rstest/coverage-istanbul -D

deno add npm:@rstest/coverage-istanbul -D

@rstest/coverage-istanbul is powered by swc-plugin-coverage-instrument. Rstest instruments source files through SWC during transform, so this provider has good transform-time performance. It can use more runtime memory because executed modules keep the injected coverage counters.

#Excluding code

Use coverage.exclude when a whole file, generated file group, or injected script should not be instrumented:

import { defineConfig } from '@rstest/core';

export default defineConfig({
  coverage: {
    enabled: true,
    provider: 'istanbul',
    exclude: ['**/src/injected-script.ts', '**/src/**/*.{worker,evaluate}.ts'],
  },
});

You can also pass the same patterns from the CLI for a one-off run:

npx rstest run --coverage --coverage.exclude "**/src/injected-script.ts" --coverage.exclude "**/src/**/*.{worker,evaluate}.ts"

Use Istanbul ignore comments only for small snippets that must stay in an otherwise covered file:

/* istanbul ignore file */

export function createInjectedScript() {
  return `globalThis.__APP_READY__ = true;`;
}

/* istanbul ignore next */
function browserEvaluateFn() {
  return window.location.href;
}

/* istanbul ignore if */
if (process.env.NODE_ENV === 'test') {
  setupTestOnlyState();
}

/* istanbul ignore else */
if (hasNativeFeature()) {
  useNativeFeature();
} else {
  useFallback();
}

If an ignored snippet still receives an injected cov_* call, use coverage.exclude for the source file instead.

#Serialized functions and other realms

Istanbul injects cov_* coverage counter calls into instrumented files. Those counters are scoped to the transformed module that Rstest executes. If code from an instrumented file is serialized and executed somewhere else, the new scope or realm may not have the matching cov_* helper, and the test can fail with ReferenceError: cov_... is not defined.

This can happen when a function is serialized with fn.toString() or executed through APIs such as page.evaluate, Worker, node:vm, eval, or new Function.

To avoid the failure, prefer one of these approaches:

• exclude the source file with coverage.exclude;
• switch to coverage.provider: 'v8' for non-browser tests;
• avoid serializing Istanbul-instrumented functions.

The v8 provider is not available in Browser Mode, so browser tests should use coverage.exclude or avoid serializing instrumented functions.

#V8 provider

The v8 provider collects precise coverage from the Node.js inspector, then remaps it to Istanbul format. Compared with Istanbul instrumentation, V8 coverage usually has lower runtime memory usage because executed modules do not need extra coverage counters. It is a better fit for large non-browser test suites where coverage memory pressure is the bottleneck.

To enable V8 coverage, install @rstest/coverage-v8 first.

npm add @rstest/coverage-v8 -D

yarn add @rstest/coverage-v8 -D

pnpm add @rstest/coverage-v8 -D

bun add @rstest/coverage-v8 -D

deno add npm:@rstest/coverage-v8 -D

Because the underlying coverage data comes from Node.js / V8 itself, remapped branch coverage and uncovered line details can vary slightly across different Node.js or V8 versions.

#Ignore hints

The v8 provider honors ignore hints when converting V8 coverage to Istanbul format. The hint prefix can be any of the following forms:

/* istanbul ignore next */
/* c8 ignore next */
/* v8 ignore next */
/* node:coverage ignore next */

Prefer using one prefix consistently in a project. The supported hint forms are:

/* v8 ignore next */
const value = optionalExpensivePath();

/* v8 ignore if */
if (process.env.NODE_ENV === 'test') {
  setupTestOnlyState();
}

/* v8 ignore else */
if (hasNativeFeature()) {
  useNativeFeature();
} else {
  useFallback();
}

/* v8 ignore start */
const generatedLookup = createGeneratedLookup();
/* v8 ignore stop */

ignore file is also recognized, but it applies to the generated coverage entry before source-map remapping. In normal Rstest output, one generated chunk can contain multiple source files, so prefer coverage.exclude when a source file or generated file group should be excluded.

The v8 provider is only available outside Browser Mode, including node, jsdom, and happy-dom test environments. Browser Mode does not use inspector coverage, so browser coverage should use the default istanbul provider.

#include

• Type: string[]
• Default: undefined
• CLI: --coverage.include <pattern>

A list of glob patterns that should be included for coverage collection. Repeat the CLI flag to specify multiple patterns.

By default, rstest will only collect coverage for files that are tested. If you want to include untested files in the coverage report, you can use the include option to specify the files or patterns to include.

Note that you should use standard glob syntax here. For a single extension, write src/**/*.ts instead of src/**/*.{ts}. Single-value braces are treated literally by the underlying glob libraries, so src/**/*.{ts} will not match .ts files.

import { defineConfig } from '@rstest/core';

export default defineConfig({
  coverage: {
    enabled: true,
    include: ['src/**/*.{js,jsx,ts,tsx}'],
  },
});

#changed

• Type: boolean | string
• Default: undefined
• CLI: --coverage.changed, --coverage.changed=<commit>

Collect coverage only for files changed in the current Git repository. Pass a commit or branch to collect coverage for files changed since that ref.

This option is available in both config and CLI:

• Use coverage.changed in rstest.config.ts when you want a persistent default, for example in CI.
• Use --coverage.changed for one-off local or CI runs.

coverage.changed only limits the coverage report scope. It does not change which tests are executed.

That means these two commands do different things:

npx rstest run --changed
npx rstest run --coverage.changed

• --changed changes the test selection and runs tests related to changed files.
• --coverage.changed keeps the normal test selection, but only reports coverage for changed source files.

#Interaction with --changed

• When --changed is used and coverage.changed is not configured, coverage reports inherit the changed files collected by --changed.
• If --changed hits forceRerunTriggers, Rstest reruns the full test suite. Coverage stays full in that case unless coverage.changed is explicitly enabled.
• If you want to use --changed for test selection but still keep full coverage reports, set coverage.changed to false in config.

Common setups:

import { defineConfig } from '@rstest/core';

export default defineConfig({
  coverage: {
    enabled: true,
    changed: 'origin/main',
  },
});

The example above still runs the normal test suite, but the coverage report only includes files changed since origin/main.

import { defineConfig } from '@rstest/core';

export default defineConfig({
  coverage: {
    enabled: true,
    changed: 'HEAD~1',
  },
});

npx rstest run --changed --coverage
npx rstest run --coverage.changed
npx rstest run --coverage.changed=HEAD~1
npx rstest run --coverage.changed=origin/main

• npx rstest run --changed --coverage runs changed-related tests and, by default, also limits coverage to the same changed file set.
• npx rstest run --coverage.changed=HEAD~1 runs the normal test suite but only reports coverage for files changed since HEAD~1.
• npx rstest run --coverage.changed=origin/main is useful when your branch is based on main: it still runs the normal test suite, but the coverage report only includes files changed compared with origin/main.

#exclude

• Type: string[]
• CLI: --coverage.exclude <pattern>
• Default:

[
  '**/node_modules/**',
  '**/__tests__/**',
  '**/__mocks__/**',
  '**/*.d.ts',
  '**/*.{test,spec}.[jt]s',
  '**/*.{test,spec}.[cm][jt]s',
  '**/*.{test,spec}.[jt]sx',
  '**/*.{test,spec}.[cm][jt]sx',
];

A glob pattern array to exclude files from test coverage collection. Repeat the CLI flag to specify multiple patterns.

Any patterns specified here will be merged with default values.

Rstest does not exclude directories named test by default. This avoids accidentally dropping source files from packages or workspaces whose path contains a test segment, such as packages/test/src/index.ts. To exclude those directories from coverage, add an explicit pattern such as test/** or **/test/**.

import { defineConfig } from '@rstest/core';

export default defineConfig({
  coverage: {
    enabled: true,
    exclude: ['**/node_modules/**', '**/dist/**'],
  },
});

#reporters

• Type: CoverageReporter[]
• Default: ['text', 'html', 'clover', 'json']
• CLI: --coverage.reporters <reporter>

The reporters to use for coverage collection. Rstest uses the standard Istanbul reporter API instead of a Rstest-specific coverage reporter API.

Each reporter can be either a string (the reporter name), a tuple with the reporter name and its options, or an Istanbul-compatible reporter object with an execute(context) method.

The CLI supports reporter names only. Repeat the flag to specify multiple reporters:

npx rstest run --coverage.reporters text --coverage.reporters=json

• See Istanbul Reporters for available reporters.
• See @types/istanbul-reports for details about reporter specific options.

import { defineConfig } from '@rstest/core';

export default defineConfig({
  coverage: {
    enabled: true,
    reporters: [
      'html',
      ['text', { skipFull: true }],
      ['json', { file: 'coverage-final.json' }],
    ],
  },
});

#Custom coverage reporters

Custom coverage reporters should follow the Istanbul reporter contract. A reporter package or file is loaded by Rstest's coverage provider (using istanbul-reports when possible), constructed with the options from coverage.reporters, and then called with an Istanbul report context.

For example, an ESM reporter can export a class with an execute method. The context parameter is Istanbul's Context type from istanbul-lib-report:

export default class CustomCoverageReporter {
  constructor(options = {}) {
    this.options = options;
  }

  /** @param {import('istanbul-lib-report').Context} context */
  execute(context) {
    // Use the standard Istanbul report context.
    const summary = context.getTree('flat').getRoot().getCoverageSummary();
    console.log('Coverage summary:', summary.toJSON());
  }
}

Then reference the reporter by package name or file path in rstest.config.ts:

import { defineConfig } from '@rstest/core';

export default defineConfig({
  coverage: {
    enabled: true,
    reporters: [
      'text',
      ['./custom-coverage-reporter.mjs', { outputFile: 'summary.json' }],
    ],
  },
});

You can also pass an Istanbul-compatible reporter object directly when the reporter is created in config:

import { defineConfig } from '@rstest/core';

export default defineConfig({
  coverage: {
    enabled: true,
    reporters: [
      {
        execute(context) {
          const summary = context
            .getTree('flat')
            .getRoot()
            .getCoverageSummary();
          console.log(summary.toJSON());
        },
      },
    ],
  },
});

#reportsDirectory

• Type: string
• Default: './coverage'
• CLI: --coverage.reportsDirectory <dir>

The directory to store coverage reports.

import { defineConfig } from '@rstest/core';

export default defineConfig({
  coverage: {
    enabled: true,
    reportsDirectory: './coverage-reports',
  },
});

#reportOnFailure

• Type: boolean
• Default: false
• CLI: --coverage.reportOnFailure

Whether to report coverage and check thresholds when tests fail.

import { defineConfig } from '@rstest/core';
export default defineConfig({
  coverage: {
    enabled: true,
    reportOnFailure: true,
  },
});

#allowExternal

• Type: boolean
• Default: false
• CLI: --coverage.allowExternal

Whether to collect coverage for source files outside the project root directory. This is useful in monorepo setups where tests import modules from sibling packages.

By default, rstest excludes files outside the project root from coverage reports, which aligns with the behavior of Jest and Vitest.

import { defineConfig } from '@rstest/core';

export default defineConfig({
  coverage: {
    enabled: true,
    allowExternal: true,
  },
});

#clean

• Type: boolean
• Default: true
• CLI: --coverage.clean, --coverage.clean=false

Whether to clean the coverage directory before running tests.

import { defineConfig } from '@rstest/core';

export default defineConfig({
  coverage: {
    enabled: true,
    clean: true,
  },
});

#thresholds

• Type:

type CoverageThreshold = {
  statements?: number;
  functions?: number;
  branches?: number;
  lines?: number;
};

type CoverageThresholds = CoverageThreshold & {
  /** check thresholds for matched files */
  [glob: string]: CoverageThreshold & {
    perFile?: boolean;
  };
};

• Default: undefined

Coverage thresholds for enforcing minimum coverage requirements. You can set thresholds for statements, functions, branches, and lines.

Thresholds specified as a positive number are taken to be the minimum percentage required. Thresholds specified as a negative number represent the maximum number of uncovered entities allowed.

import { defineConfig } from '@rstest/core';

export default defineConfig({
  coverage: {
    enabled: true,
    thresholds: {
      statements: 80,
      functions: 80,
      branches: 80,
      lines: -10,
    },
  },
});

When the code coverage is below the specified thresholds, the test will fail and output an error message like below:

Error: Coverage for statements 75% does not meet global threshold 80%
Error: Coverage for functions 75% does not meet global threshold 80%
Error: Coverage for branches 75% does not meet global threshold 80%
Error: Uncovered lines 20 exceeds maximum global threshold allowed 10

#glob pattern

If globs are specified, thresholds will be checked for each matched file pattern. If the file specified by path is not found, an error is returned.

import { defineConfig } from '@rstest/core';

export default defineConfig({
  coverage: {
    enabled: true,
    thresholds: {
      // Thresholds for matching glob pattern
      'src/**': {
        statements: 100,
      },
      'node/**/*.js': {
        statements: 90,
      },
      // Thresholds for all files
      statements: 80,
    },
  },
});

Following the above configuration, rstest will fail if:

• The total code coverage of all files in src/** is below 100%.
• The total code coverage of all files in node/**/*.js is below 90%.
• The global code coverage is below 80% for statements.

#check threshold for per file

Rstest also supports checking thresholds for each matched file by setting perFile to true.

import { defineConfig } from '@rstest/core';

export default defineConfig({
  coverage: {
    enabled: true,
    thresholds: {
      'src/**': {
        statements: 90,
        perFile: true,
      },
    },
  },
});