@systemfsoftware/stryker-js-typescript-checker

TypeScript checker plugin for Stryker mutation testing — provides native support for TypeScript 5.x through 7.x.

Why Use a Type Checker Plugin?

Mutation testing modifies code syntax in ways that may cause compiler errors (e.g. invalid type assignments, breaking return type contracts). Without a checker plugin, those mutants execute in your test runner, waste runner execution time, or trigger misleading test runner errors.

The TypeScript checker intercepts mutants before they reach the test runner. If a mutant causes a TypeScript compilation failure, it is classified immediately as CompileError without spinning up test runner workers.

Prerequisites

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

Install

pnpm add -D @systemfsoftware/stryker-js-typescript-checker typescript

Setup in stryker.config.ts

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

export default defineConfig({
  checkers: ['typescript'],
  plugins: ['@systemfsoftware/stryker-js-typescript-checker'],
  // Optional custom tsconfig path (defaults to tsconfig.json)
  // tsConfigFile: 'tsconfig.build.json',
})

In-process runtime (./runtime)

The default entry is the worker plugin Stryker loads from plugins, and that is all a normal setup needs. Tooling that drives the compiler itself — for example an oracle that instruments a project and hands the mutants to the real checker — can import the in-process runtime from the ./runtime subpath instead:

import { CheckerRuntime, nodes, TypeScriptCompiler } from '@systemfsoftware/stryker-js-typescript-checker/runtime'

It publishes the runtime Layer (CheckerRuntime.layer(options)), its CheckerRuntimeShape type, the TypeScriptCompiler service tag and the nodes program-graph accessor. Everything else stays behind the worker entry.

License

Apache-2.0