Karma plugin to allow tests to be distributed across multiple browsers

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4.4.06 years ago6 years agoMinified + gzip package size for karma-sharding in KB


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Karma plugin to allow tests to be distributed across multiple browsers


This is intended to avoid the memory usage problems seen with some browsers and numerous or memory intensive specs. Lower your concurrency setting if total memory is a problem running in parallel processes.
You can pass configuration to override these defaults:
  sharding: {
    specMatcher: /(spec|test)s?\.js/i,
    base: '/base',
    getSets: function(config, basePath, files) {
        // splitForBrowsers - some util function
        return splitForBrowsers(files.served)
            .map(oneBrowserSet => [someInitScript].concat(oneBrowserSet));
getSets might be overridden when files from karma.files config should be organized in certain view, for example:
karma.files has set - [setup.js, one.unit.js, two.unit.js] - and it must be combined for each browser as [setup.js, one.unit.js] and [setup.js, two.unit.js]


The easiest way is to install karma-sharding as a devDependency, by running
npm install karma karma-sharding --save-dev



// karma.conf.js
module.exports = function(config) {
    files: [

    frameworks: ['sharding'], // this will load the framework and beforeMiddleware

    preprocessors: {
      // source files, that you wanna generate coverage for
      // do not include tests or libraries
      // (these files will be instrumented by Istanbul)
      'src/**/*.js': ['coverage'] // coverage is loaded from karma-coverage by karma-sharding

    // sharding replaces the coverage reporter inline to allow the preprocessor to run
    // preprocessor:coverage looks for reporter:coverage otherwise it would use a unique name
    reporters: ['progress', 'coverage'],

    browsers: ['ChromeHeadless', 'ChromeHeadless'] // this will split the tests into two sets

For more information on Karma see the homepage.