Karma plugin which runs your mocha tests in a WebWorker

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Karma plugin which runs your mocha tests in a WebWorker.
Using this plugin you can test your javascript code for WebWorker compatibility.


Install the module and save it as a devDependency:
npm install karma-mocha-webworker --save-dev

Instructions on how to install karma can be found here.
You will then have to configure your karma config:
module.exports = config => {
    // 1. Load this karma plugin
    frameworks : ['mocha-webworker'],

    // 2. Configure the files you would like karma to serve.
    //    Make sure you set `included` to `false`. Otherwise karma
    //    will execute your scripts outside of the WebWorker.
    files      : [
      {pattern: 'test/my-test-case.js', included: false},
      {pattern: 'test/more-test-cases/*.js', included: false}

    client     : {
      // 3. Configure the URLs that this plugin should execute
      //    within a WebWorker for you. These patterns are
      //    matched (using minimatch) on the `config.files`
      //    array configured in step 2.
      //    If you omit `pattern`, all URLs will be executed.
      mochaWebWorker: {
        pattern : [
        // You can also use a SharedWorker for test execution
        // instead of the default 'Worker'
        worker: 'SharedWorker',
        // You can also pass some options to mocha:
        mocha   : {
          ui: 'tdd'
        // You can also evaluate javascript code within the Worker at various stages:
        evaluate: {
          beforeMochaImport: 'self.console.log("Before the mocha script is imported")',
          beforeMochaSetup : 'self.console.log("Before mocha is setup (mocha.setup())")',
          beforeScripts    : 'self.console.log("Before your scripts are imported")',
          beforeRun        : 'self.console.log("Before your tests are run (mocha.run())")',
          afterRun         : 'self.console.log("After your tests have been run")'


To run only some test cases matching a given pattern, you can use:
karma start &
karma run -- --grep foo

Google Chrome Caveat

Google Chrome currently (tested up to v55) does not pass on stack information when an error occurs within a script loaded into a Web Worker (e.g. importScripts(['foo.js'])). So if your script contains a syntax error or a runtime error, the stack will point at a line within karma-mocha-webworker. You can workaround this issue by using Firefox.