cypress/system-tests/projects/plugin-event-deprecated/cypress.config.js

module.exports = {
  'e2e': {
    'supportFile': false,
    setupNodeEvents (on, config) {
      if (config.env.NO_MUTATE_RETURN) {
        on('before:browser:launch', (browser, options) => {
          // this will emit a warning
          options = [...options, '--foo']

          return options
        })

        return
      }

      if (config.env.CONCAT_RETURN) {
        on('before:browser:launch', (browser, options) => {
          // this will emit a warning
          options = options.concat(['--foo'])

          return options
        })

        return
      }

      if (config.env.NO_WARNING) {
        on('before:browser:launch', (browser, options) => {
          // this will NOT emit a warning
          options.args.push('--foo')
          options.args.push('--bar')

          return options
        })

        return
      }

      on('before:browser:launch', (browser, options) => {
        // this will emit a warning
        options.push('--foo')
        options.push('--bar')

        return options
      })

      return config
    },
  },
}