async command () {
    // Other Nightwatch commands are available via "this.api"
    this.api.init()
    this.api.waitForElementVisible('#app')

    const result = await this.api.elements('css selector', '#app ul')
    assert.strictEqual(result.value.length, 3)
  }
A class-based Nightwatch custom command which is a variation of the openHomepage.js command.
 The command name is the filename and class needs to contain a "command" method.

Example usage:
  browser.openHomepageClass();

For more information on writing custom commands see:
  https://nightwatchjs.org/guide/extending-nightwatch/#writing-custom-commands