.alerts.setText() 編集を提案

                    .alerts.setText(value, [callback])
                

module.exports = {
  'set text on JS prompt': function (browser) {
    browser
      .alerts.setText('some text', function () {
        console.log('text sent to JS prompt successfully');
      });
  },

  'set text on JS prompt with ES6 async/await': async function (browser) {
    await browser.alerts.setText('some text');
  }
};