karma.conf.js

const coverage = process.env.COVERAGE;

// configures browsers to run test against
// any of [ 'ChromeHeadless', 'Chrome', 'Firefox', 'IE', 'PhantomJS' ]
const browsers = (process.env.TEST_BROWSERS || 'ChromeHeadless').split(',');

const singleStart = process.env.SINGLE_START;

// use puppeteer provided Chrome for testing
process.env.CHROME_BIN = require('puppeteer').executablePath();

const suite = coverage ? 'test/coverageBundle.js' : 'test/testBundle.js';

module.exports = function (karma) {
  const config = {
    frameworks: ['webpack', 'mocha', 'sinon-chai'],

    files: [suite],

    preprocessors: {
      [suite]: ['webpack', 'env'],
    },

    reporters: ['spec'].concat(coverage ? 'coverage' : []),

    specReporter: {
      maxLogLines: 10,
      suppressSummary: true,
      suppressErrorSummary: false,
      suppressFailed: false,
      suppressPassed: false,
      suppressSkipped: true,
      showBrowser: false,
      showSpecTiming: false,
      failFast: false,
    },

    coverageReporter: {
      reporters: [{ type: 'lcov', subdir: '.' }],
    },

    browsers,

    singleRun: true,
    autoWatch: false,

    webpack: {
      mode: 'development',
      resolve: {
        mainFields: ['module', 'browser', 'main'],
        modules: ['node_modules', __dirname],
        alias: {
          react: 'preact/compat',
          'react-dom': 'preact/compat',
        },
      },
      module: {
        rules: [
          {
            test: /\.js$/,
            enforce: 'pre',
            use: ['source-map-loader'],
          },
          {
            test: /\.s[ac]ss$/i,
            use: ['css-loader', 'sass-loader'],
          },
          {
            test: /\.css$/,
            use: 'raw-loader',
          },
          {
            test: /\.m?js$/,
            exclude: /node_modules/,
            use: {
              loader: 'babel-loader',
              options: {
                plugins: [
                  [
                    '@babel/plugin-transform-react-jsx',
                    {
                      importSource: 'preact',
                      runtime: 'automatic',
                    },
                  ],
                  '@babel/plugin-transform-react-jsx-source',
                ].concat(
                  coverage
                    ? [
                        [
                          'istanbul',
                          {
                            include: ['src/**'],
                          },
                        ],
                      ]
                    : [],
                ),
              },
            },
          },
          {
            test: /\.svg$/,
            use: ['@svgr/webpack'],
          },
        ],
      },
      devtool: 'eval-source-map',
    },
  };

  if (singleStart) {
    config.browsers = [].concat(config.browsers, 'Debug');
    config.envPreprocessor = [].concat(config.envPreprocessor || [], 'SINGLE_START');
  }

  karma.set(config);

  process.env.TZ = 'Europe/Berlin';
};