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    wct-mocha makes testing your web components a breeze!

    You get a streamlined browser-based testing environment, designed to work with web-component-tester or on its own.

    # Getting Started

    Install mocha and wct-mocha as devDependencies

    $ npm install --save-dev mocha
    $ npm install --save-dev wct-mocha

    Install web-component-tester or polymer-cli globally

    $ npm install --global web-component-tester
    $ npm install --global polymer-cli

    Run wct or polymer test

    $ wct --npm
    $ polymer test --npm

    .html Suites

    Your test suites can be .html documents. For example, test/awesomest-tests.html:

    <!doctype html>
      <meta charset="utf-8">
      <script src="../node_modules/@webcomponents/webcomponentsjs/webcomponents-loader.js"></script> 
      <script src="../node_modules/mocha/mocha.js"></script> 
      <script src="../node_modules/chai/chai.js"></script> 
      <script src="../node_modules/@polymer/test-fixture/test-fixture.js"></script> 
      <script src="../node_modules/wct-mocha/wct-mocha.js"></script> 
      <awesome-element id="fixture"></awesome-element>
      <script type="module">
        import {AwesomeElement} from '../src/awesome-element.js';
        suite('<awesome-element>', () => {
          test('is awesomest', () => {
            const element = document.getElementById('fixture');

    .js Suites

    Alternatively, you can write tests in separate .js sources. For example, test/awesome-tests.js:

    suite('AwesomeLib', () => {
      test('is awesome', () => {

    Special Features

    Nested Suites

    To help support this case, you can also directly define an index that will load any desired tests:

    <!doctype html>
        <meta charset="utf-8">
        <script src="../node_modules/@webcomponents/webcomponentsjs/webcomponents-loader.js"></script> 
        <script src="../node_modules/mocha/mocha.js"></script> 
        <script src="../node_modules/wct-mocha/wct-mocha.js"></script> 

    When you use wct or polymer test on the command line, it is generating an index like this for you based on the suites you ask it to load.

    Web Components Support

    By default, WCT will defer tests until the WebComponentsReady event has been emitted by @webcomponents/webcomponents-loader.js or one of its polyfill bundles. This saves you from having to wait for elements to upgrade and all that yourself.

    If you need to test something that occurs before that event, the testImmediate helper can be used.

    Alternately, if you are not using the @webcomponents/webcomponentjs polyfills or loader or otherwise simply want tests to run as soon as possible, you can disable this delay by setting WCT.waitForFrameworks = false (though, they are still async due to Mocha).


    WCT supports Mocha's TDD (suite/test/etc) and BDD (describe/it/etc) interfaces, and will call mocha.setup/mocha.run for you. Just write your tests, and you're set.

    Custom Environments

    If you would like to have WCT load libraries on your behalf, you can define a list of scripts to load. There are two ways of doing this:

    Inside your test code (before wct-mocha/wct-mocha.js is loaded):

      WCT = {
        environmentScripts: [
          // Include anything else that you like!

    Alternatively, web-component-tester can pass the entire value of the WCT block object here straight from the clientOptions key in wct.conf.json.

    A reference of the default configuration can be found at browser/config.ts.

    Use any web server

    If you prefer not to use WCT's command line tool, you can also run WCT tests directly in a browser via a web server of your choosing and still make use of all of its features.

    Make sure that the wct-mocha/wct-mocha.js script is accessible by your web server, and have your tests load it after loading mocha/mocha.js.


    npm i wct-mocha

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