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Karma Runner


A plugin to use the karma test runner (or @angular/cli's ng test) in Stryker.


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

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

Bring your own test runner

The @stryker-mutator/karma-runner is a plugin for stryker to enable karma as a test runner. However, it does not come packaged with it's own version of karma, instead it uses your very own karma version. It can also work with @angular/cli, see Configuring

Note: karma v2.0.3 has a known issue which makes it impossible to use it with Stryker. please upgrade to 2.0.4 or higher.


You can configure the @stryker-mutator/karma-runner using the stryker.config.json (or stryker.config.js) config file.

"testRunner": "karma",
"karma": {
"projectType": "custom",
"configFile": "path/to/karma.conf.js",
"config": {
"browsers": ["ChromeHeadless"]

karma.projectType ["custom" | "angular-cli"]

Default: "custom"

Specify which kind of project you're using. This determines which command is used to start karma

  • "custom": configure @stryker-mutator/karma-runner to use karma start.
  • "angular-cli": configure @stryker-mutator/karma-runner to use ng test (see configuring for angular-cli).

karma.configFile [string]

Default: undefined

Specify a 'karma.conf.js' file to be loaded. Options specified directly in your stryker.config.js file using karma.config will overrule options in your karma.conf.js file.

karma.config [object]

Default: undefined

Specify karma configuration options directly. Options specified here will overrule any options in your karma.conf.js file.

karma.ngConfig.testArguments [object]

Default: undefined

Add ng test arguments. For example, specify an alternative project with:

"karma": {
"projectType": "angular-cli",
"ngConfig": {
"testArguments": {
"project": "my-lib"

This will run ng test with --project argument: ng test --project=my-lib.

Non overridable options

The browser's life cycle is determined by @stryker-mutator/karma-runner. I.e. these settings cannot be overridden. You configuration settings for these will be ignored.

browserNoActivityTimeout: 1000000,
autoWatch: false,
singleRun: false,
detached: false

The coverage plugin will also be removed (not needed for mutation testing).

Configure angular cli

Please follow the angular guide.


As Stryker runs karma in its own process, its logging output will be consumed by Stryker.

To see all logging from karma, set the log level to trace in stryker.config.json.

"logLevel": "trace"