web-test-runner.config.js

/**
 * @license
 * Copyright 2021 Google LLC
 * SPDX-License-Identifier: BSD-3-Clause
 */

import { legacyPlugin } from '@web/dev-server-legacy'
import { playwrightLauncher } from '@web/test-runner-playwright'

const mode = process.env.MODE || 'dev'
if (!['dev', 'prod'].includes(mode)) {
  throw new Error(`MODE must be "dev" or "prod", was "${mode}"`)
}

const browsers = {
  // Local browser testing via playwright
  // ===========
  chromium: playwrightLauncher({ product: 'chromium' }),
  firefox: playwrightLauncher({ product: 'firefox' })
}

// Prepend BROWSERS=x,y to `npm run test` to run a subset of browsers
// e.g. `BROWSERS=chromium,firefox npm run test`
const noBrowser = (b) => {
  throw new Error(`No browser configured named '${b}'; using defaults`)
}
let commandLineBrowsers
try {
  commandLineBrowsers = process.env.BROWSERS?.split(',').map(
    (b) => browsers[b] ?? noBrowser(b)
  )
} catch (e) {
  console.warn(e)
}

// https://modern-web.dev/docs/test-runner/cli-and-configuration/
export default {
  rootDir: '.',
  files: ['./test/**/*_test.js'],
  nodeResolve: { exportConditions: mode === 'dev' ? ['development'] : [] },
  preserveSymlinks: true,
  browsers: commandLineBrowsers ?? Object.values(browsers),
  testFramework: {
    // https://mochajs.org/api/mocha
    config: {
      ui: 'tdd'
    }
  },
  plugins: [
    // Detect browsers without modules (e.g. IE11) and transform to SystemJS
    // (https://modern-web.dev/docs/dev-server/plugins/legacy/).
    legacyPlugin({
      polyfills: {
        webcomponents: true,
        // Inject lit's polyfill-support module into test files, which is required
        // for interfacing with the webcomponents polyfills
        custom: [
          {
            name: 'lit-polyfill-support',
            path: 'node_modules/lit/polyfill-support.js',
            test: "!('attachShadow' in Element.prototype) || !('getRootNode' in Element.prototype) || window.ShadyDOM && window.ShadyDOM.force",
            module: false
          }
        ]
      }
    })
  ]
}