Use Karma, Mocha, Chai and Coverage to run headless unit tests and generate lcov code coverage

Github: https://github.com/railsstudent/image-gallery-native-js

1) Install gulp, mocha, chai, puppeteer, http-server as dev-dependencies

yarn add gulp mocha chai puppeteer http-server -D

2) Install all karma dependencies as dev-dependencies.

yarn add karma karma-chai karma-mocha karma-chrome-launcher mocha chai -D

3) Create test/bootstrap.karma.js file to share global variables among unit test cases.

'use strict';
 
const expect = chai.expect;
const assert = chai.assert;

4) Run karma command to generate karma.conf.js to specify Karma configuration.

./node_modules/.bin/karma init
// Karma configuration
// Generated on Sun Aug 26 2018 09:31:46 GMT+0800 (HKT)
 
process.env.CHROME_BIN = require('puppeteer').executablePath();
module.exports = function(config) {
  config.set({
 
    // base path that will be used to resolve all patterns (eg. files, exclude)
    basePath: '',
 
    plugins: [
      "karma-chai",
      "karma-chrome-launcher",
      "karma-mocha",
      "karma-coverage"
    ],
 
    // frameworks to use
    // available frameworks: https://npmjs.org/browse/keyword/karma-adapter
    frameworks: ['mocha', 'chai'],
 
    // list of files / patterns to load in the browser
    files: [
      'src/**/*.js',
      'test/bootstrap.karma.js',
      'test/**.test.js'
    ],
 
    // list of files / patterns to exclude
    exclude: [
      'test/gallery.test.js'
    ],
 
    // preprocess matching files before serving them to the browser
    // available preprocessors: https://npmjs.org/browse/keyword/karma-preprocessor
    preprocessors: {
      'src/**/!(gallery).js': 'coverage'
    },
 
    // optionally, configure the reporter
    coverageReporter: {
      type : 'lcov',
      dir : 'coverage/',
      subdir: '.'
    },
 
    // test results reporter to use
    // possible values: 'dots', 'progress'
    // available reporters: https://npmjs.org/browse/keyword/karma-reporter
    reporters: ['progress', 'coverage'],
 
    // enable / disable watching file and executing tests whenever any file changes
    autoWatch: false,
 
    // start these browsers
    // available browser launchers: https://npmjs.org/browse/keyword/karma-launcher
    browsers: ['ChromeHeadless'],
 
    // Continuous Integration mode
    // if true, Karma captures browsers, runs the tests and exits
    singleRun: true,
  })
}

Explicitly list karma plugins for chai, browser launcher, mocha and code coverage.

plugins: [
   "karma-chai",
   "karma-chrome-launcher",
   "karma-mocha",
  "karma-coverage"
 ]

Include mocha and chai required by the unit test cases.

// frameworks to use
// available frameworks: https://npmjs.org/browse/keyword/karma-adapter
frameworks: ['mocha', 'chai'],

Load src/, test/bootstrap.karma.js and test/**/*.test.js in browser. Exclude test/gallery.test.js since this test file contains automated UI test cases

// list of files / patterns to load in the browser
files: [
  'src/**/*.js',
  'test/bootstrap.karma.js',
  'test/**.test.js'
],
 
// list of files / patterns to exclude
exclude: [
  'test/gallery.test.js'
]

Use Chromium instance of puppeteer to execute headless browser test

process.env.CHROME_BIN = require('puppeteer').executablePath();
browsers: ['ChromeHeadless'],

Add lcov code coverage. Code coverage results are kept in coverage/lcov-report directory

preprocessors: {
 'src/**/!(gallery).js': 'coverage'
},
 
// optionally, configure the reporter
coverageReporter: {
   type : 'lcov',
   dir : 'coverage/',
   subdir: '.'
}

Add reporters for headless browser testing and code coverage

reporters: ['progress', 'coverage']

5) Install gulp-karma to integrate karma with gulp

yarn add gulp-karma -D

Add gulp test task to run karma test runner

/**
 * Run test once and exit
 */
gulp.task('test', function (done) {
    new KarmaServer({
        configFile: __dirname + '/karma.conf.js',
        singleRun: true
    }, done).start();
});

6) Set up npm script commands in package.json.

"scripts": {
   "test": "gulp test",
   "serve:coverage": "gulp test && http-server coverage/lcov-report/ -p 8001"
}

Test unit test cases in headless browser

yarn test

Serve lcov code coverage results at http://localhost:8001

yarn serve:coverage

7) Write mocha test case in test file.

'use strict';
 
describe('slideshow test', function() {
  let first, middle;
  let imageUrls = [];
  let slideshow = null;
  before(function() {
    first = 0;
    middle = 1;
  });
 
  describe('single image slideshow', () => {
    before(function() {
      // runs before all tests in this block
      imageUrls = [
        'image1.jpg'
      ];
      slideshow = new SlideShow(imageUrls);
      slideshow.setCurrentIndex(first);
    });
 
    it('slideshow has 1 image', function() {
      assert.strictEqual(slideshow.totalCount(), imageUrls.length);
    });
 
    it('current url should be the first url', function() {
      assert.strictEqual(slideshow.currentUrl(), 'image1.jpg');
    });
 
    it('initial index is always 0', function() {
      assert.strictEqual(slideshow.currentIndex(), first);
    });
 
    it('Slide show with 1 image is always the first image', function() {
      assert.strictEqual(slideshow.isFirstImage(), true);
    });
 
    it('Slide show with 1 image is always last image', function() {
      assert.strictEqual(slideshow.isLastImage(), true);
    });
 
    it('Show next image does nothing when there is 1 image', function() {
      assert.strictEqual(slideshow.showNext(), false);
      assert.strictEqual(slideshow.currentIndex(), first);
    });
 
    it('Slide prev image with 1 image is always last image', function() {
      assert.strictEqual(slideshow.showPrev(), false);
      assert.strictEqual(slideshow.currentIndex(), first);
    });
  });
});

Finally, we are done.