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Mocha Runner

A plugin to use Mocha in Stryker


Install @stryker-mutator/mocha-runner locally within your project folder, like so:

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

Peer dependencies

The @stryker-mutator/mocha-runner is a plugin for stryker to enable mocha as a test runner. As such, you should make sure you have the correct versions of its dependencies installed:

  • mocha
  • @stryker-mutator/core


You can configure the mocha test runner in the stryker.config.json (or stryker.config.js) file.

"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": ".*"

When using Mocha version 6, @stryker-mutator/mocha-runner will use mocha's internal file loading mechanism to load your mocha configuration. So feel free to leave out the mochaOptions entirely if you're using one of the default file locations.

Alternatively, use ['no-config']: true, ['no-package']: true or ['no-opts']: true to ignore the default mocha config, default mocha package.json and default mocha opts locations respectively.

mochaOptions.spec [string or string[]]

Default: "test/**/*.js"

Choose which files to include. This is comparable to mocha's test directory although there is no support for --recursive.

If you want to load all files recursively: use a globbing expression ('test/**/*.js'). If you want to decide on the order of files, use multiple globbing expressions. For example: use ['test/helpers/**/*.js', 'test/unit/**/*.js'] if you want to make sure your helpers are loaded before your unit tests.

mochaOptions.config [string | undefined]

Default: undefined

Explicit path to the mocha config file

New since Mocha 6

mochaOptions.package [string | undefined]

Default: undefined

Specify an explicit path to a package.json file (ostensibly containing configuration in a mocha property). See

New since Mocha 6

mochaOptions.opts [string | false]

Default: "test/mocha.opts"

Specify a 'mocha.opts' file to be loaded. Options specified directly in your stryker.config.js file will overrule options from the 'mocha.opts' file. Disable loading of an additional mocha.opts file with false.

The only supported mocha options are used: --ui, --require, --async-only, --timeout, --grep (or their short form counterparts). Others are ignored by the @stryker-mutator/mocha-runner.

mochaOptions.grep [RegExp]

Default: undefined

Specify a mocha grep command, to single out individual tests.

mochaOptions.ui [string]

Default: undefined

Set the name of your mocha ui

mochaOptions.extension [string]

Default: undefined

Set mocha's --extension property.

mochaOptions.require [string[]]

Default: []

Set mocha's require option

Note: if you want to require esm, you will need to use "testRunnerNodeArgs": ["--require", "esm"] instead. See #3014 for more information.

mochaOptions.async-only [boolean]

Default: false

Set mocha's asyncOnly option

mochaOptions.timeout [number]

Default: undefined

Set mocha's timeout option