Stryker JS

https://github.com/stryker-mutator/stryker-js
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StrykerJS is a mutation testing framework for JavaScript, designed to improve code quality by...
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### Install and initialize Stryker

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/getting-started.md

Run npm init stryker@latest to install Stryker and start the initializer, which asks questions to configure your project.

```bash
npm init stryker@latest
```

--------------------------------

### Install dependencies with npm install

Source: https://github.com/stryker-mutator/stryker-js/blob/master/e2e/test/vue-typescript-vitest/README.md

Install the project dependencies using npm. Run this in the project root before using the other scripts.

```bash
npm install
```

--------------------------------

### Install grunt-stryker and dependencies

Source: https://github.com/stryker-mutator/stryker-js/blob/master/packages/grunt-stryker/README.md

Install the required packages for using grunt-stryker with Grunt.

```bash
npm install stryker stryker-api grunt-stryker --save-dev
```

--------------------------------

### Install @stryker-mutator/core

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/guides/vuejs.md

Install the core Stryker package using npm or yarn.

```bash
npm i -D @stryker-mutator/core
```

```bash
yarn add --dev @stryker-mutator/core
```

--------------------------------

### inPlace command line example

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/configuration.md

Enables in-place mutation via the command line.

```bash
--inPlace
```

--------------------------------

### Install StrykerJS and run with defaults

Source: https://github.com/stryker-mutator/stryker-js/blob/master/README.md

Install StrykerJS and run it with default settings for small projects. It uses 'npm test' as the test command and mutates files in the 'lib' and 'src' directories.

```bash
pnpm add --save-dev @stryker-mutator/core
# Only for small projects:
npx stryker run
```

--------------------------------

### Config file usage example - stryker.conf.js

Source: https://github.com/stryker-mutator/stryker-js/blob/master/packages/grunt-stryker/README.md

Content of the stryker.conf.js file used in the config file example.

```javascript
// stryker.conf.js
module.exports = {
  files: [{ pattern: 'src/**/*.js', mutated: true} , 'test/myFirstFile.spec.js', 'test/mySecondFile.spec.js'],
  testFramework: 'jasmine',
  testRunner: 'karma'
};
```

--------------------------------

### logLevel command line example

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/configuration.md

Sets the log level via the command line.

```bash
--logLevel info
```

--------------------------------

### logLevel config file example

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/configuration.md

Sets the log level via the config file. Default is 'info'.

```json
"logLevel": "info"
```

--------------------------------

### Install @stryker-mutator/vitest-runner

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/guides/vuejs.md

Install the Vitest runner plugin for Stryker using npm or yarn.

```bash
npm i -D @stryker-mutator/vitest-runner
```

```bash
yarn add --dev @stryker-mutator/vitest-runner
```

--------------------------------

### Install @stryker-mutator/tap-runner

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/tap-runner.md

Install the tap runner plugin locally within your project folder using npm.

```shell
npm i --save-dev @stryker-mutator/tap-runner
```

--------------------------------

### Install @stryker-mutator/jest-runner with npm or yarn

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/jest-runner.md

Install the plugin locally in your project. Use either npm or yarn.

```bash
npm i --save-dev @stryker-mutator/jest-runner
# OR
yarn add --dev @stryker-mutator/jest-runner
```

--------------------------------

### Example stryker.config.json with mocha test runner

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/config-file.md

Example config file specifying the mocha test runner and per-test coverage analysis.

```json
{
  "$schema": "./node_modules/@stryker-mutator/core/schema/stryker-schema.json",
  "testRunner": "mocha",
  "coverageAnalysis": "perTest"
}
```

--------------------------------

### inPlace config file example

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/configuration.md

Enables in-place mutation via the config file. Default is false.

```json
"inPlace": true
```

--------------------------------

### incrementalFile command line example

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/configuration.md

Sets the file used for incremental mode via the command line.

```bash
--incrementalFile reports/stryker-incremental-alternative.json
```

--------------------------------

### Example code with console.debug statements to ignore

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/disable-mutants.md

Shows a pair of functions with console.debug statements that a user may want to ignore mutants in. The surrounding text notes that ignoring these via `// Stryker disable` comments gets tedious, motivating the ignore-plugin approach.

```js
function add(a, b) {
  console.debug('add called');
  return a + b;
}
function subtract(a, b) {
  console.debug('subtract called');
  return a + b;
}
```

--------------------------------

### Install @stryker-mutator/mocha-runner

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/mocha-runner.md

Install the @stryker-mutator/mocha-runner plugin locally within your project folder.

```shell
npm i --save-dev @stryker-mutator/mocha-runner
```

--------------------------------

### Express routes and supertest test suite for parallel worker conflict example

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/parallel-workers.md

Example application and test suite used to illustrate port conflicts when Stryker runs parallel workers. The routes.js file defines GET /home and POST /echo endpoints; index.test.js starts the server on port 4444 and tests both routes with supertest.

```javascript
// routes.js

const express = require('express');
const router = express.Router();

router.get('/home', (_req, res) => res.send('Hello World!'))

router.post('/echo', (req, res) => res.json(req.body))

module.exports = router
```

```javascript
// index.test.js

const server = require('../src/index.js');
const supertest = require('supertest');
 
describe("API tests", () => {
    
    let app;
    let port = 4444

     beforeAll(() => {
        app = server.listen(port);
     });

     afterAll(() => {
        app.close();
     });

    test("GET /home", async () => {
        await supertest(server).get("/home")
            .expect(200)
            .then((response) => expect(response.text).toBe('Hello World!'));
    });

    test("POST /echo - non-empty request body", async () => {
        const body = { "john": "doe", "marilyn": "monroe" }
        await supertest(server).post("/echo")
            .send(body)
            .expect(200)
            .then((response) => expect(response.body).toStrictEqual(body));
    });
    
});
```

--------------------------------

### jsonReporter config file example

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/configuration.md

Configures the json reporter's output file name.

```json
"jsonReporter": { "fileName": "coverage/stryker.json" }
```

--------------------------------

### ignorePatterns negation example

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/configuration.md

Use the ! prefix to undo an ignore pattern, for example to stop ignoring node_modules.

```text
["!node_modules"]
```

--------------------------------

### Stryker config file example

Source: https://github.com/stryker-mutator/stryker-js/blob/master/packages/grunt-stryker/README.md

Example of a Stryker config file that exports a function accepting a config object, used as an alternative to Gruntfile configuration.

```javascript
module.exports = function(config){
  config.set({
    files: ['src/**/*.js', 'test/myFirstFile.spec.js', 'test/mySecondFile.spec.js'],
    mutate: ['src/**/*.js'],
    logLevel: 'debug'
  });
}
```

--------------------------------

### Install @stryker-mutator/karma-runner with npm

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/karma-runner.md

Install the plugin locally within the project folder using npm. Use this command to add @stryker-mutator/karma-runner as a dev dependency.

```bash
npm i --save-dev @stryker-mutator/karma-runner
```

--------------------------------

### Configure dashboard reporter in config file

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/configuration.md

Configuration file example for the dashboard reporter. Sets the project, version, module, baseUrl, and reportType options.

```json
{
  "dashboard": {
    "project": "github.com/my-org/my-project",
    "version": "branch-or-tag",
    "module": "my-module",
    "baseUrl": "https://dashboard.stryker-mutator.io/api/reports",
    "reportType": "full"
  }
}
```

--------------------------------

### Install @stryker-mutator/typescript-checker

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/typescript-checker.md

Install the TypeScript checker plugin as a dev dependency using npm.

```bash
npm install --save-dev @stryker-mutator/typescript-checker
```

--------------------------------

### Config file usage example - Gruntfile.js

Source: https://github.com/stryker-mutator/stryker-js/blob/master/packages/grunt-stryker/README.md

Configure grunt-stryker to use a config file via the configFile option.

```javascript
// Gruntfile.js
grunt.initConfig({
  stryker: {
    jasmine: {
      options: {
        configFile: 'stryker.conf.js'
      }
    },
  },
});
```

--------------------------------

### maxTestRunnerReuse command line example

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/configuration.md

Sets the maximum test runner reuse via the command line.

```bash
--maxTestRunnerReuse 20
```

--------------------------------

### Navigate to project root

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/getting-started.md

Open a terminal and change to the root of your project before installing Stryker.

```bash
cd my-project
```

--------------------------------

### Compile and hot-reload for development with npm run dev

Source: https://github.com/stryker-mutator/stryker-js/blob/master/e2e/test/vue-typescript-vitest/README.md

Starts the Vite development server with hot module replacement for local development.

```bash
npm run dev
```

--------------------------------

### Install @stryker-mutator/api as a dev dependency

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/disable-mutants.md

Installs the @stryker-mutator/api package as a dev dependency, which is required before declaring an ignore-plugin.

```shell
npm i -D @stryker-mutator/api
```

--------------------------------

### Install @stryker-mutator/jasmine-runner with npm

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/jasmine-runner.md

Install the plugin locally as a dev dependency. Requires jasmine and @stryker-mutator/core as peer dependencies.

```bash
npm i --save-dev @stryker-mutator/jasmine-runner
```

--------------------------------

### mutate command line examples

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/configuration.md

Configures the files to mutate via the command line. Supports globbing patterns, negation, and specific files.

```bash
--mutate "src/**/*.js", "a.js"
```

```bash
-m "src/**/*.js", "a.js"
```

```bash
--mutate "src/**/*.ts","!src/**/*.spec.ts","!src/**/*.module.ts"
```

```bash
--mutate src/app/home/home.component.ts
```

```bash
--mutate "src/app/home/*.ts","!src/app/home/*.spec.ts"
```

--------------------------------

### mutate config file examples

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/configuration.md

Configures the files to mutate via the config file. Supports globbing patterns and negation.

```json
"mutate": ["src/**/*.js", "a.js"]
```

```json
"mutate": ["src/**/*.ts","!src/**/*.spec.ts","!src/**/*.module.ts"]
```

--------------------------------

### incrementalFile config file example

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/configuration.md

Sets the file used for incremental mode via the config file. Default is 'reports/stryker-incremental.json'.

```json
"incrementalFile": "reports/stryker-incremental-alternative.json"
```

--------------------------------

### Install @stryker-mutator/api dependency

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/guides/create-a-plugin.md

Install the @stryker-mutator/api package as a dependency for your plugin. This provides the types and basic helper functionality needed to create a Stryker plugin.

```shell
npm install @stryker-mutator/api
```

--------------------------------

### Install @stryker-mutator/cucumber-runner with npm

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/cucumber-runner.md

Install the plugin locally within your project folder using npm. Use this command to add @stryker-mutator/cucumber-runner as a development dependency.

```shell
npm i --save-dev @stryker-mutator/cucumber-runner
```

--------------------------------

### ignorePatterns command line example

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/configuration.md

Use the --ignorePatterns CLI flag to pass comma-separated glob patterns. This overrides the config file setting.

```text
--ignorePatterns dist,coverage
```

--------------------------------

### Default options usage example

Source: https://github.com/stryker-mutator/stryker-js/blob/master/packages/grunt-stryker/README.md

Run mutation testing with default options, using jasmine and karma, with source and test file patterns.

```javascript
grunt.initConfig({
  stryker: {
    jasmine: {
      files: {
        src: ['src/**/*.js'],
        tests: ['test/**/*.js', '!test/IgnoredTestFile.js']
      },
      mutate: {
        src: ['src/**/*.js']
      }
    },
    options: {
        testFramework: 'jasmine',
        testRunner: 'karma'
    }
  },
});
```

--------------------------------

### Install local StrykerJS packages with install-local

Source: https://github.com/stryker-mutator/stryker-js/blob/master/CONTRIBUTING.md

Use install-local to link local StrykerJS packages into your project. Include core, util, api, instrumenter, and the plugin you need (here jest-runner).

```sh
cd my-project
npx install-local ../stryker-js/packages/core ../stryker-js/packages/util ../stryker-js/packages/api ../stryker-js/packages/instrumenter ../stryker-js/packages/jest-runner
```

--------------------------------

### StrykerJS configuration to load a local plugin

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/guides/create-a-plugin.md

Example StrykerJS configuration for loading a local plugin. Set the testRunner, checkers, and reporters to your plugin names, and add the plugin path to the plugins array. Use testRunnerNodeArgs and checkerNodeArgs with --inspect to debug your plugins in their child processes. Ensure your TypeScript is compiled before running.

```js
{
  // name of your test runner
  "testRunner": "foo", 
  // name of your checker
  "checkers": ["bar"], 
  // name your reporter
  "reporters": ["progress", "my-reporter"], 
  // load your test runner, reporter or checker plugin here
  "plugins": ["@stryker-mutator/*", "../my-plugin"], 
  // useful for debugging your 
  "concurrency": 1, 
  // useful for debugging your test runner plugin
  "testRunnerNodeArgs": ["--inspect"], 
  // useful for debugging your checker plugin
  "checkerNodeArgs": ["--inspect"]
};
```

--------------------------------

### Run Stryker with trace logging

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/getting-started.md

Use npx stryker run --logLevel trace to get more detailed logs when troubleshooting issues.

```bash
npx stryker run --logLevel trace
```

--------------------------------

### All mutants survive with module-alias

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/troubleshooting.md

Example output showing all mutants surviving when using module-alias, with a survived ArithmeticOperator mutant and a 0.00% mutation score.

```text
[...]
#3. [Survived] ArithmeticOperator
C:\z\github\stryker-mutator\stryker-js\e2e\test\jest-node\src\sum.js:5:10
-     return a - b;
+     return a + b;
Ran all tests for this mutant.

Ran 0.00 tests per mutant on average.
----------|---------|----------|-----------|------------|----------|---------|
File      | % score | # killed | # timeout | # survived | # no cov | # error |
----------|---------|----------|-----------|------------|----------|---------|
All files |    0.00 |        0 |         0 |          4 |        0 |       0 |
 sum.js   |    0.00 |        0 |         0 |          4 |        0 |       0 |
----------|---------|----------|-----------|------------|----------|---------|
```

--------------------------------

### Stryker config for typescript-checker

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/troubleshooting.md

Configuration options to add to Stryker's config file to enable the typescript-checker plugin. Install it with `npm install --save-dev @stryker-mutator/typescript-checker`.

```json
{
  "checkers": ["typescript"],
  "tsconfigFile": "tsconfig.json"
}
```

--------------------------------

### Incremental analysis statistics output

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/incremental.md

Example output shown after the dry run when incremental mode is enabled. It reports the number of changed mutant files and test files, and the total number of mutant results that can be reused.

```text
        Mutants:        1 files changed (+2 -2)
        Tests:          2 files changed (+22 -21)
        Result:         3731 of 3965 mutant result(s).
```

--------------------------------

### maxTestRunnerReuse config file example

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/configuration.md

Sets the maximum test runner reuse via the config file. Default is 0 (infinite reuse).

```json
"maxTestRunnerReuse": 20
```

--------------------------------

### mutate mutation range examples

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/configuration.md

Specifies exact code blocks to mutate using mutation ranges. Ranges are postfixed to the file path.

```text
"src/app.js:1-11"
```

```text
"src/app.js:5:4-6:4"
```

```text
"src/app.js:5-6:4"
```

--------------------------------

### ignorePatterns config file example

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/configuration.md

Configure ignorePatterns in the Stryker config file to specify glob patterns for files or directories that should not be copied to the sandbox. The default is an empty array.

```json
"ignorePatterns": ["dist", "coverage"]
```

--------------------------------

### Mutant schemata example after instrumentation

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/guides/create-a-plugin.md

The simplified result of Stryker's mutant schemata step, where all mutants are placed into the code simultaneously and only one can be active at a time. Shows the generated cover function and the mutated add function with active mutant switching.

```javascript
function cover(id) {
  if (global.__stryker__.activeTest) {
    global.__stryker__.mutantCoverage.perTest[global.__stryker__.activeTest][id]++;
  }
  else {
    global.__stryker__.mutantCoverage.static.[id]++;
  }
}

function add(a, b) {
  if (global.__stryker__.activeMutant === 0) {
    // 👾
  } else {
    cover(0);
    return global.__stryker__.activeMutant === 1
      ? a - b // 👽
      : (cover(1), a + b);
  }
}
```

--------------------------------

### Configure typescript checker in stryker.config.json

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/typescript-checker.md

Example configuration for the TypeScript checker in stryker.config.json. Sets the checker to typescript, points to the tsconfig file, and enables prioritizing performance over accuracy.

```json
{
  "checkers": ["typescript"],
  "tsconfigFile": "tsconfig.json",
  "typescriptChecker": {
    "prioritizePerformanceOverAccuracy": true
  }
}
```

--------------------------------

### Configure jasmine test runner in stryker.config.json

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/jasmine-runner.md

Example configuration for the jasmine test runner in the `stryker.config.json` (or `stryker.config.js`) file. Sets coverage analysis to perTest, the test runner to jasmine, and points to the jasmine configuration file.

```json
{
  "coverageAnalysis": "perTest",
  "testRunner": "jasmine",
  "jasmineConfigFile": "spec/support/jasmine.json"
}
```

--------------------------------

### JavaScript heap out of memory error log

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/troubleshooting.md

Example log output showing the JavaScript heap out of memory error when running Stryker mutations. The solution is to limit the number of workers by setting `--concurrency` in the stryker config.

```text
16:58:25 (17452) INFO ConfigReader Using stryker.config.json
16:58:26 (17452) INFO InputFileResolver Found 2 of 2557 file(s) to be mutated.
16:58:27 (17452) INFO Instrumenter Instrumented 2 source file(s) with 118 mutant(s)
16:58:28 (17452) INFO ConcurrencyTokenProvider Creating 6 checker process(es) and 5 test runner process(es).
16:59:40 (17452) INFO DryRunExecutor Starting initial test run. This may take a while.
16:59:53 (17452) INFO DryRunExecutor Initial test run succeeded. Ran 72 tests in 13 seconds (net 250 ms, overhead 12910 ms).
Mutation testing  [  ] 12% (elapsed: ~1m, remaining: ~7m) 15/118 tested (0 survived, 10 timed out)
<--- Last few GCs --->
[17452:0000022998429D50]    75135 ms: Scavenge 302.2 (313.0) -> 295.2 (313.0) MB, 0.8 / 0.2 ms  (average mu = 0.992, current mu = 0.975) task
[17452:0000022998429D50]   125511 ms: Scavenge 302.0 (313.0) -> 295.9 (313.2) MB, 1.3 / 0.0 ms  (average mu = 0.992, current mu = 0.975) task
[17452:0000022998429D50]   149148 ms: Scavenge 296.5 (301.2) -> 296.0 (301.7) MB, 2.3 / 0.2 ms  (average mu = 0.992, current mu = 0.975) allocation failure
<--- JS stacktrace --->
FATAL ERROR: Committing semi space failed. Allocation failed - JavaScript heap out of memory
 1: 00007FF61D741DDF napi_wrap+109135
 2: 00007FF61D6E6D06 v8::internal::OrderedHashTable<v8::internal::OrderedHashSet,1>::NumberOfElementsOffset+33350
```

--------------------------------

### Declare a value plugin with declareValuePlugin

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/guides/create-a-plugin.md

Declares a Stryker plugin as a value using declareValuePlugin. Practical for simple plugins like an ignore-plugin. This example ignores console.x statements by returning a message from shouldIgnore.

```ts
// index.ts
import { declareValuePlugin, PluginKind } from '@stryker-mutator/api/plugin';

export const strykerPlugins = [declareValuePlugin(PluginKind.Ignore, 'console', {
  shouldIgnore(path) {
    if (
      path.isExpressionStatement() &&
      path.node.expression.type === 'CallExpression' &&
      path.node.expression.callee.type === 'MemberExpression' &&
      path.node.expression.callee.object.type === 'Identifier' &&
      path.node.expression.callee.object.name === 'console'
    ) {
      return "We're not interested in testing `console.x` statements, see ADR 648.";
    }
  }
})];
```

--------------------------------

### TypeScript checker error TS2717

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/troubleshooting.md

Example error that may occur after adding the typescript-checker and running `npx stryker run`. To fix it, add `"skipLibCheck": true` to your tsconfig file.

```text
node_modules/@types/react/index.d.ts:3075:13 - error TS2717: Subsequent property declarations must have the same type.  Property 'rt' must be of type 'DetailedHTMLProps<HTMLAttributes<HTMLElement>, HTMLElement>', but here has type 'DetailedHTMLProps<HTMLAttributes<HTMLElement>, HTMLElement>'.
```

--------------------------------

### FooTestRunner plugin with typed-inject DI

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/guides/create-a-plugin.md

Example of a test runner plugin using typed-inject for dependency injection. The class injects commonTokens (logger, options) and pluginTokens (configLoader, processEnv). The factory method provides the plugin tokens and injects the class. TypedInject validates that injected tokens exist at runtime.

```ts
import { StrykerOptions } from '@stryker-mutator/api/core';
import { Logger } from '@stryker-mutator/api/logging';
import { commonTokens, PluginContext } from '@stryker-mutator/api/plugin';
import { TestRunner, DryRunResult, DryRunOptions, MutantRunOptions, MutantRunResult, TestRunnerCapabilities } from '@stryker-mutator/api/test-runner';
import * as pluginTokens from './plugin-tokens';
import FooTestRunnerConfigFileLoader from './foo-test-runner-config-file-loader';

export class FooTestRunner implements TestRunner {
  public static inject = [
    commonTokens.logger,
    commonTokens.options,
    pluginTokens.configLoader,
    pluginTokens.processEnv
  ] as const;
  
  constructor(
    private readonly log: Logger,
    private readonly options: StrykerOptions,
    private readonly configLoader: FooTestRunnerConfigFileLoader,
    private readonly processEnvRef: NodeJS.ProcessEnv,
  ) { }

  public capabilities(): TestRunnerCapabilities {
    return { reloadEnvironment: false };
  }

  public init(): Promise<void> {
    // TODO: Implement or remove
  }
  
  public dryRun(options: DryRunOptions): Promise<DryRunResult> {
   // TODO: Implement
  }
  
  public mutantRun(options: MutantRunOptions): Promise<MutantRunResult> {
    // TODO: Implement
  }
  
  public dispose(): Promise<void> {
   // TODO: Implement or remove
  }
}


export function fooTestRunnerFactory(injector: Injector<PluginContext>) {
  return injector
    .provideValue(pluginTokens.processEnv, process.env)
    .provideClass(pluginTokens.configLoader, FooTestRunnerConfigFileLoader)
    .injectClass(FooTestRunner);
}
fooTestRunnerFactory.inject = [commonTokens.injector] as const;
```

--------------------------------

### Disable comment syntax

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/disable-mutants.md

Syntax for the disable comment. The comment starts with // Stryker, followed by disable or restore, optionally next-line, a mutator list (comma-separated or all), and an optional custom reason after a colon.

```plaintext
// Stryker [disable|restore] [next-line] *mutatorList*[: custom reason]
```

--------------------------------

### ArrayMutation mutant not compilable

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/troubleshooting.md

Example of an ArrayMutation mutant generated by StrykerJS that is not compilable by TypeScript. The TypeScript compiler would report an error like 'Type 'any[][]' is not assignable to type 'ComponentData[]'.

```ts
let typesWithLabelsObjects: ComponentData[] = new Array([]);
```

--------------------------------

### Format with Prettier

Source: https://github.com/stryker-mutator/stryker-js/blob/master/e2e/test/vue-typescript-vitest/README.md

Runs the formatter using Prettier.

```bash
npm run format
```

--------------------------------

### Fix port conflict using STRYKER_MUTATOR_WORKER environment variable

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/parallel-workers.md

Diff showing the fix for port conflicts: use the STRYKER_MUTATOR_WORKER environment variable to offset the port. The variable is set by Stryker to a unique number starting from 0 and incremented by 1 for each worker.

```diff
-  let port = 4444
+  let port = 4444 + (+process.env.STRYKER_MUTATOR_WORKER || 0)
```

--------------------------------

### Checkout git submodules

Source: https://github.com/stryker-mutator/stryker-js/blob/master/perf/README.md

Commands to initialize and update git submodules for the performance test projects.

```bash
git submodule init 
git submodule update
```

--------------------------------

### Run unit tests with vitest

Source: https://github.com/stryker-mutator/stryker-js/blob/master/e2e/test/vue-typescript-vitest/README.md

Runs the unit tests using vitest.

```bash
npm run test:unit
```

--------------------------------

### Stryker CLI general usage syntax

Source: https://github.com/stryker-mutator/stryker-js/blob/master/README.md

General usage syntax for the StrykerJS CLI. Run 'npx stryker' followed by a command, options, and an optional configuration file.

```sh
$ npx stryker <command> [options] [configFile]
```

--------------------------------

### buildCommand config file

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/configuration.md

Configures a build command to run after mutating the code.

```json
"buildCommand": 'npm run build'
```

--------------------------------

### Run Stryker with npx

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/usage.md

The main command for Stryker is 'run', which kicks off mutation testing. By default, Stryker looks for a stryker.config.json, stryker.config.js, or other variations in the current working directory, which can be overridden by specifying a different file as the last argument.

```sh
npx stryker <command> [options] [configFile]
```

--------------------------------

### Run Stryker programmatically with StrykerCli and Stryker

Source: https://github.com/stryker-mutator/stryker-js/blob/master/packages/core/README.md

Shows how to use both `StrykerCli` and `Stryker` programmatically. `StrykerCli.run()` does not return a promise and may call `process.exit`; `Stryker` accepts a partial options object and `runMutationTest()` returns a promise that resolves with mutant results or rejects with an error.

```ts
async function main() {
  // Runs Stryker as if it was called directly from the cli. Not even returns a promise, it assumes to be allowed to call `process.exit`.
  new StrykerCli(process.argv /* RAW argv array */ ).run(); 

  // Runs Stryker, will not assume to be allowed to exit the process.
  const stryker = new Stryker({ concurrency: 4 } /* Partial Stryker options object */ );
  const mutantResults = await stryker.runMutationTest();
  // mutantResults or rejected with an error.
}
```

--------------------------------

### Create stryker.config.json

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/guides/vuejs.md

Configuration file for Stryker with Vitest runner and plugin.

```json
{
  "$schema": "./node_modules/@stryker-mutator/core/schema/stryker-schema.json",
  "testRunner": "vitest",
  "plugins": ["@stryker-mutator/vitest-runner"]
}
```

--------------------------------

### mutantRun with mutantActivation and reloadEnvironment

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/guides/create-a-plugin.md

Illustrates how to handle mutant activation and environment reloading in the mutantRun method. The mutantActivation can be 'static' or 'runtime', and the reloadEnvironment boolean controls whether to reload source and test files.

```ts
mutantRun(options: MutantRunOptions): Promise<MutantRunResult> {
  if(options.mutantActivation === 'static') {
    global.__stryker__.activeMutant = options.activeMutant.id;
  }
  if(options.reloadEnvironment || this.notLoadedTheEnvironmentYet){
    this.loadTestFiles();
  }
  if(options.mutantActivation === 'runtime'){
    global.__stryker__.activeMutant = options.activeMutant.id;
  }
  return runFilteredTests(options.testFilter);
}
```

--------------------------------

### Lint with ESLint

Source: https://github.com/stryker-mutator/stryker-js/blob/master/e2e/test/vue-typescript-vitest/README.md

Runs the linter using ESLint.

```bash
npm run lint
```

--------------------------------

### Type-check, compile and minify for production with npm run build

Source: https://github.com/stryker-mutator/stryker-js/blob/master/e2e/test/vue-typescript-vitest/README.md

Builds the application for production, including type checking via vue-tsc.

```bash
npm run build
```

--------------------------------

### Build for production

Source: https://github.com/stryker-mutator/stryker-js/blob/master/e2e/test/angular-project/src/app/app.component.html

Builds the Angular application for production using the production configuration.

```bash
ng build --prod
```

--------------------------------

### Run end-to-end tests with cypress

Source: https://github.com/stryker-mutator/stryker-js/blob/master/e2e/test/vue-typescript-vitest/README.md

Runs the end-to-end tests using Cypress.

```bash
npm run test:e2e
```

--------------------------------

### FooTestRunner implements TestRunner

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/guides/create-a-plugin.md

Creates a plugin class that implements the TestRunner interface. The init method is a placeholder to implement or remove.

```ts
import { TestRunner, DryRunResult, DryRunOptions, MutantRunOptions, MutantRunResult } from '@stryker-mutator/api/test-runner';

class FooTestRunner implements TestRunner {
  public init(): Promise<void> {
    // TODO: Implement or remove
  }
  
  public dryRun(options: DryRunOptions): Promise<DryRunResult> {
    // TODO: Implement or remove
  }

  public mutantRun(options: MutantRunOptions): Promise<MutantRunResult> {
    // TODO: Implement or remove```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```json,json```
```

--------------------------------

### Vitest configuration for Stryker

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/guides/svelte.md

Create a stryker.config.json file with the testRunner set to 'vitest' for Svelte projects using Vitest.

```json
{
  "testRunner": "vitest"
}
```

--------------------------------

### Configure buildCommand for tap runner

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/tap-runner.md

Shows a diff of the Stryker configuration for the tap runner. Add a buildCommand to compile TypeScript with tsc, update testFiles to point to the compiled JavaScript in dist/test, and remove nodeArgs and the original testFiles entries.

```diff
{
  "buildCommand": "tsc",
  "tap": {
    "testFiles": ["dist/test/**/*.js"],
    "nodeArgs": ["--import", "tsx"],
    "testFiles": ["test/**/*.ts"]
  }
}
```

--------------------------------

### Basic Stryker configuration for Angular with Karma

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/guides/angular.md

Basic configuration for Angular projects using Karma as the test runner. Created by the `npm init stryker@latest` command as `stryker.config.json` or `stryker.config.mjs`. Requires @angular/cli 9.0.0 or higher.

```json
{
  "$schema": "./node_modules/@stryker-mutator/core/schema/stryker-schema.json",
  "packageManager": "npm",
  "reporters": ["html", "clear-text", "progress"],
  "testRunner": "karma",
  "coverageAnalysis": "perTest"
}
```

--------------------------------

### Run Stryker with default or custom config file

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/config-file.md

Shell commands to run Stryker. The first uses default config file names, the second specifies a custom config file as a second argument.

```shell
# Use default config file names in the current working directory
npx stryker run
# Use "alternative-stryker.config.json"
npx stryker run alternative-stryker.config.json
```

--------------------------------

### Generate a new component with Angular CLI

Source: https://github.com/stryker-mutator/stryker-js/blob/master/e2e/test/angular-project/src/app/app.component.html

Use this command to scaffold a new component in an Angular project. It creates the component files and registers it in the nearest module.

```bash
ng generate component xyz
```

--------------------------------

### Run Stryker with --inPlace

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/troubleshooting.md

Alternative workaround for module-alias: run Stryker with the --inPlace flag to mutate files in place.

```bash
npx stryker run --inPlace
```

--------------------------------

### Jest configuration for Stryker

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/guides/svelte.md

Create a stryker.config.json file with the testRunner set to 'jest' for Svelte projects using Jest.

```json
{
  "testRunner": "jest"
}
```

--------------------------------

### Run Stryker mutation tests

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/getting-started.md

Execute npx stryker run to mutation test your project.

```bash
npx stryker run
```

--------------------------------

### Run Stryker with local plugin via stryker.conf.json

Source: https://github.com/stryker-mutator/stryker-js/blob/master/CONTRIBUTING.md

Run Stryker from the command line in your test project after adding the local plugin path to stryker.conf.json. If using the typescript checker, add its local path to the plugins array to avoid the 'Cannot find Checker plugin "typescript"' error.

```sh
cd my-project
open stryker.conf.json
 # Add `"plugins": ["/home/username/stryker-js/packages/karma-runner/dist/src/index.js"]` inside the stryker.conf.json
 #   If you use typescript checker and you get an error :  Cannot find Checker plugin "typescript"
 #   then add the typescript checker local path to the `plugin` as well:
 #   "plugins": ["/Users/username/stryker-js/packages/karma-runner/dist/src/index.js",  "/Users/username/stryker-js/packages/typescript-checker/dist/src/index.js"],
/home/username/stryker-js/packages/core/bin/stryker run
```

--------------------------------

### Jest configuration with experimental VM modules

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/guides/svelte.md

If using native ESM, add the '--experimental-vm-modules' flag to testRunnerNodeArgs in the stryker.config.json file.

```diff
{
  "testRunner": "jest",
+ "testRunnerNodeArgs": ["--experimental-vm-modules"]
}
```

--------------------------------

### Run tests

Source: https://github.com/stryker-mutator/stryker-js/blob/master/e2e/test/angular-project/src/app/app.component.html

Runs the unit tests for the Angular application using Karma.

```bash
ng test
```

--------------------------------

### Load grunt-stryker plugin in Gruntfile

Source: https://github.com/stryker-mutator/stryker-js/blob/master/packages/grunt-stryker/README.md

Enable the grunt-stryker plugin in your Gruntfile.

```javascript
grunt.loadNpmTasks('grunt-stryker');
```

--------------------------------

### allowConsoleColors command line flag

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/configuration.md

Enables or disables colors in the console output. Defaults to true.

```bash
--allowConsoleColors true
```

--------------------------------

### stryker.config.json with schema and comment

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/config-file.md

Minimal JSON config file with schema reference and a comment property. The '_comment' property is a convention for comments in JSON.

```json
{
  "$schema": "./node_modules/@stryker-mutator/core/schema/stryker-schema.json",
  "_comment": "Comments can be put inside `xxx_comment` properties."
}
```

--------------------------------

### Import source file in test

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/troubleshooting.md

Import your source file directly in your test file so Vitest can find related test files.

```ts
import '../src/file-under-test.ts';
```

--------------------------------

### Add test:mutation script to package.json

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/guides/vuejs.md

Script to run Stryker mutation testing.

```json
{
  "scripts": {
    "test:mutation": "stryker run"
  }
}
```

--------------------------------

### Configure tap test runner in stryker.config.json

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/tap-runner.md

Configure the tap test runner in stryker.config.json. Sets testFiles glob, nodeArgs for tsx, and forceBail to true.

```json
{
  "testRunner": "tap",
  "tap": {
    "testFiles": ["test/**/*.@(js|ts)"],
    "nodeArgs": ["--import", "tsx"],
    "forceBail": true
  }
}
```

--------------------------------

### allowConsoleColors config file

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/configuration.md

Sets the allowConsoleColors option in the Stryker configuration file.

```json
"allowConsoleColors": true
```

--------------------------------

### Add dependency placeholder

Source: https://github.com/stryker-mutator/stryker-js/blob/master/e2e/test/angular-project/src/app/app.component.html

Placeholder command for adding a dependency with the Angular CLI. Replace the blank with the actual package name.

```bash
ng add _____
```

--------------------------------

### appendPlugins config file

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/configuration.md

Configures additional plugins for Stryker to load without overwriting the default plugins.

```json
"appendPlugins": ["my_plugin"]
```

--------------------------------

### Enable ESM support with testRunnerNodeArgs

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/jest-runner.md

Add the --experimental-vm-modules node option to the Stryker configuration to enable Jest's ECMAScript Modules (ESM) support.

```json
{
  "testRunnerNodeArgs": ["--experimental-vm-modules"]
}
```

--------------------------------

### Add plugins to Stryker config for pnpm

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/troubleshooting.md

Add the plugins array to your Stryker configuration to explicitly load plugins when using pnpm, since pnpm's directory structure prevents auto-detection.

```diff
{
  "packageManager": "pnpm",
  "testRunner": "jest",
  "checkers": ["typescript"],
+  "plugins": [
+    "@stryker-mutator/jest-runner",
+    "@stryker-mutator/typescript-checker"
+  ]
}
```

--------------------------------

### Run Stryker with incremental mode

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/incremental.md

Enable incremental mutation testing by passing the --incremental flag to the stryker run command. The equivalent configuration option is "incremental": true in stryker.config.json.

```bash
npx stryker run --incremental
```

--------------------------------

### Add PWA support with Angular CLI

Source: https://github.com/stryker-mutator/stryker-js/blob/master/e2e/test/angular-project/src/app/app.component.html

Adds Progressive Web App support to the Angular application using the Angular CLI.

```bash
ng add @angular/pwa
```

--------------------------------

### Add Angular Material to the project

Source: https://github.com/stryker-mutator/stryker-js/blob/master/e2e/test/angular-project/src/app/app.component.html

Adds Angular Material to the project, including its schematics and dependencies.

```bash
ng add @angular/material
```

--------------------------------

### allowEmpty command line flag

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/configuration.md

Enables the allowEmpty option from the command line. Prevents the test runner from exiting with an error when no tests are executed during the initial dry run.

```text
--allowEmpty
```

--------------------------------

### Configure sandbox for module-alias

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/troubleshooting.md

Workaround to keep using module-alias: mark node_modules as part of the sandbox by adding ignorePatterns and setting symlinkNodeModules to false.

```diff
{
+  "ignorePatterns": ["!node_modules"],
+  "symlinkNodeModules": false
}
```

--------------------------------

### testFiles CLI usage

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/configuration.md

Command line flag to limit which test files are executed during mutation testing. Only tests from these files will be run.

```bash
--testFiles "foo/tests/**/*.spec.js","bar/tests/**/*.test.js"
```

--------------------------------

### allowEmpty config file

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/configuration.md

Sets the allowEmpty option in the Stryker configuration file. Prevents the test runner from exiting with an error when no tests are executed during the initial dry run.

```json
"allowEmpty": true
```

--------------------------------

### Configure jest options in Stryker config

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/jest-runner.md

Optional configuration for the Jest runner using the `jest` property. Includes `projectType`, `configFile`, `config`, and `enableFindRelatedTests`.

```json
{
  "jest": {
    "projectType": "custom",
    "configFile": "path/to/your/custom/jestConfig.js",
    "config": {
      "testEnvironment": "jest-environment-jsdom-sixteen"
    },
    "enableFindRelatedTests": true
  }
}
```

--------------------------------

### Configure mocha test runner in stryker.config.json

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/mocha-runner.md

Configure the mocha test runner in the stryker.config.json (or stryker.config.js) file. The mochaOptions object supports spec, config, package, opts, ui, require, async-only, and grep options.

```json
{
  "testRunner": "mocha",
  "coverageAnalysis": "perTest",
  "mochaOptions": {
    "spec": [ "test/**/*.js" ],
    "config": "path/to/mocha/config/.mocharc.json",
    "package": "path/to/custom/package/package.json",
    "opts": "path/to/custom/mocha.opts",
    "ui": "bdd",
    "require": [ "babel-register" ],
    "async-only": false,
    "grep": ".*"
  }
}
```

--------------------------------

### Error: Cannot find TestRunner plugin

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/troubleshooting.md

Error message shown when Stryker cannot load plugins, such as @stryker-mutator/typescript-checker, when using pnpm as package manager.

```text
Cannot find TestRunner plugin "mocha". No TestRunner plugins were loaded.
```

--------------------------------

### Import Stryker and StrykerCli

Source: https://github.com/stryker-mutator/stryker-js/blob/master/packages/core/README.md

Imports the two classes exported for programmatic use: `Stryker` and `StrykerCli`.

```ts
import { Stryker, StrykerCli } from '@stryker-mutator/core';
```

--------------------------------

### Jest multi project configuration error

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/troubleshooting.md

Error output when Jest is configured with multiple "projects" and the jest-runner uses runCli, which does not support this configuration. The workaround is to configure Jest without using "projects".

```text
 ERROR DryRunExecutor One or more tests resulted in an error:
        Test runner crashed. Tried twice to restart it without any luck. Last time the error message was:
Error: Jest: Cannot use configuration as an object without a file path.
    at readConfig (C:\z\github\jest-issue\node_modules\jest-config\build\index.js:188:13)
```

--------------------------------

### Configure vitest runner in stryker.config.json

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/vitest-runner.md

Configures the vitest test runner in the Stryker config file. The `vitest` object supports the `configFile`, `dir`, and `related` options.

```json
{
  "testRunner": "vitest",
  "vitest": {
    "configFile": "vitest.config.js",
    "dir": "packages",
    "related": true
  }
}
```

--------------------------------

### Run Stryker with npx or npm script

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/guides/nodejs.md

Use npx stryker run to execute Stryker directly, or npm run test:mutation if you have defined a custom script named test:mutation in package.json. The comment shows the alternative command.

```shell
npx stryker run
# OR, if your script is called "test:mutation"
npm run test:mutation 
```

--------------------------------

### Run build command inside Stryker sandbox

Source: https://github.com/stryker-mutator/stryker-js/blob/master/docs/troubleshooting.md

Run the build command manually inside the Stryker sandbox directory to verify it works. The sandbox directory does not contain node_modules, so you must specify the full path to the TypeScript compiler.

```shell
cd .stryker-tmp/sandbox-12345678
node ../../node_modules/typescript/bin/tsc -b path/to/tsconfig.json
```
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