@systemfsoftware/stryker-js-vitest-runner

Vitest test-runner plugin for Stryker mutation testing. Provides fast in-process sandboxing, per-test coverage tracking, and native TypeScript support.

Prerequisites

• Node.js >=22.18.0
• Vitest >=2.0.0
• @systemfsoftware/stryker-js >=5.0.0

Install

pnpm add -D @systemfsoftware/stryker-js-vitest-runner vitest

Setup in stryker.config.ts

Plugins in Stryker 5.0 take bare package names resolved from your project — no import.meta.resolve() needed:

import { defineConfig } from '@systemfsoftware/stryker-js/config'

export default defineConfig({
  testRunner: 'vitest',
  plugins: ['@systemfsoftware/stryker-js-vitest-runner'],
  mutate: [
    'src/**/*.ts',
    '!src/**/*.test.ts',
    '!src/**/*.d.ts',
  ],
})

How It Works

1. Dry-run phase: The Vitest runner executes your existing test suite, collecting per-test execution profiles and code coverage data.
2. Mutant sandbox: During the mutation test phase, worker processes run only the subset of tests that cover each mutant, terminating early on test failure to maximize speed.
3. Vitest Config: By default, Stryker automatically discovers your vitest.config.ts or vite.config.ts. If your configuration is located elsewhere, specify it in your config:

export default defineConfig({
  testRunner: 'vitest',
  plugins: ['@systemfsoftware/stryker-js-vitest-runner'],
  vitest: {
    configFile: 'vitest.unit.config.ts',
  },
})

Worker pool

The runner uses the pool your Vitest config selects. Set pool: 'threads' in the runner's options to run every test file on Vitest's isolated threads pool instead, with no child processes. This is what testRunner: 'vm' in @systemfsoftware/stryker-js does. With pool set, a Vitest config that enables browser mode for any project is refused at startup; leave pool unset to run browser-mode suites.

export default defineConfig({
  testRunner: {
    plugin: '@systemfsoftware/stryker-js-vitest-runner',
    options: { pool: 'threads' },
  },
})

In-Source Tests (import.meta.vitest)

If your project uses in-source testing with if (import.meta.vitest) blocks, add the companion ignorer plugin so unreachable test mutants are excluded from your score:

pnpm add -D @systemfsoftware/stryker-ignorer-in-source-vitest-block

export default defineConfig({
  testRunner: {
    plugin: '@systemfsoftware/stryker-js-vitest-runner',
  },
  ignorers: ['@systemfsoftware/stryker-ignorer-in-source-vitest-block'],
})

License

Apache-2.0