setup.js

function startMarionette() {
  suiteSetup(function() {
    this.timeout(10000);
    var driver = new Marionette.Drivers.HttpdPolling();
    yield driver.connect(Task.next);
    device = new Marionette.Client(driver, {
      defaultCallback: Task.next
    });
    yield device.startSession();
  });
}

suite('calendar months', function(){
  startMarionette();

  //...
})