This package has been deprecated

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Stryker v1 is released, but you're still using a 0.x version. This version is no longer maintained. Please use @stryker-mutator/wct-runner. See for the full migration guide.

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0.3.1 • Public • Published

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Stryker WCT runner


Install stryker-wct-runner locally within your project folder, like so:

npm i --save-dev stryker-wct-runner

Peer dependencies

The stryker-wct-runner is a plugin to enable the Web Component Tester (wct) as a test runner for Stryker. As such, you should make sure you have the correct versions of its dependencies installed:

  • web-component-tester
  • stryker-api

For the minimum supported versions, see the peerDependencies section in package.json.

Note for Polymer users: if you're using a global installation of polymer-cli to run your tests, you will need to install web-component-tester locally, right next to the stryker-wct-runner package. The stryker-wct-runner will not be able to find your global installation of the polymer-cli. You can use this command: npm i -D web-component-tester.


Configuring Stryker

Make sure you set the testRunner option to "wct" and set coverageAnalysis to "off" in your Stryker configuration.

    testRunner: 'wct'
    coverageAnalysis: 'off', // coverage analysis is not supported yet for the stryker-wct-runner.
    maxConcurrentTestRunners: 4, // A maximum of half your CPU's is recommended
    timeoutMS: 10000 // A higher timeout is recommended to allow for browser startup

For more information on what these options mean, take a look at the Stryker readme.

Configuring WCT

The stryker-wct-runner will honor your regular wct configuration. This means that it will automatically load the wct.conf.json file from the current working directory as expected. You can change this to a different file using the wct.configFile property in your Stryker config:

// Override config file example
wct: {
    configFile: 'config/wct.conf.json'

It is also possible to override other wct properties specific for stryker. Full example:

// Full example
wct: {
    configFile: 'alternative/wct/configuration.json',
    verbose: true,
    npm: true,
    plugins: {
        local: {
            browsers: ["chrome"],
            skipSeleniumInstall: true,
            browserOptions: {
                chrome: ["window-size=1920,1080", "headless", "disable-gpu"],
                firefox: ["--headless"]

wct.verbose [boolean]

Default: false

Enable/disable verbose WCT logging. WCT can be noisy. By default, Stryker will swallow any wct log messages. Enabling this option will forward any wct log messages to Stryker logging. Don't forget to set logLevel (or fileLogLevel) to 'debug' in your Stryker configuration to get the most logging out of WCT.

wct.npm [boolean]

Default: false

Use WCT with the --npm flag. This will allow web-components installed via npm, instead of bower.


Default: undefined

It is recommended to configure a headless browser when using WCT in combination with Stryker. An example configuration:

wct: {
    plugins: {
        local: {
          browserOptions: {
                chrome: ["window-size=1920,1080", "headless", "disable-gpu"],
                firefox: ["--headless"]

Other wct options

For more information about the available wct options, please see wct's config.ts file.

Loading the plugin

In order to use the stryker-wct-runner it must be loaded in the Stryker mutation testing framework via the Stryker configuration. The easiest way to achieve this, is not have a plugins section in your config file. That way, all node_modules starting with stryker- will be loaded.


Make sure to read the Stryker contribution guidelines located in the Stryker mono repository.

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