Before Cypress launches a browser, it gives you the ability to modify the arguments used to launch it.

This is helpful to modify, remove, or add your own arguments.

The most common use case is adding your own chrome extension.

Usage

Modify args based on browser

Using your pluginsFile you can tap into the before:browser:launch event and modify the arguments based on the browser that Cypress is launching.

This event will yield you the browser as an object, and args which are the default arguments used to launch the browser.

args may be an array or an object (based on the type of browser we’re launching). Whatever you return from this event will become the new args for launching the browser.

Here are options for the currently supported browsers:

• Chrome, Chromium, or Canary
• Electron

module.exports = (on, config) => {
  on('before:browser:launch', (browser = {}, args) => {
    // browser will look something like this
    // {
    //   name: 'chrome',
    //   displayName: 'Chrome',
    //   version: '63.0.3239.108',
    //   path: '/Applications/Google Chrome.app/Contents/MacOS/Google Chrome',
    //   majorVersion: '63'
    // }

    if (browser.name === 'chrome') {
      // `args` is an araay of all the arguments
      // that will be passed to Chrome when it launchers
      args.push('--start-fullscreen')

      // whatever you return here becomes the new args
      return args
    }

    if (browser.name === 'electron') {
      // `args` is a `BrowserWindow` options object
      // https://electronjs.org/docs/api/browser-window#new-browserwindowoptions
      args['fullscreen'] = true

      // whatever you return here becomes the new args
      return args
    }
  })
}

Examples

Use fake video for webcam testing

By default, Cypress passes the Chrome command line switch to enable a fake video for a media stream. This is to better enable testing webcam functionality without having to have the necessary hardware to test.

You can however send your own video file for testing by passing a Chrome command line switch pointing to a video file.

module.exports = (on, config) => {
  on('before:browser:launch', (browser = {}, args) => {
    if (browser.name === 'chrome') {
      // Mac/Linux
      args.push('--use-file-for-fake-video-capture=cypress/fixtures/my-video.y4m')

      // Windows
      // args.push('--use-file-for-fake-video-capture=c:\\path\\to\\video\\my-video.y4m')
    }

    return args
  })
}