PHPUnit无法运行测试

Question

执行测试时，会出现这样的错误：
This test did not perform any assertions OK, but incomplete, skipped, or risky tests!
PHPUnit 6.2.2，PHP 7.0，Selenium 3.4.0

protected $url = "https://click.alfabank.ru";
public function testSearch()
{
    $this->webDriver->get($this->url);
    sleep(20);
    $this->webDriver->findElement(WebDriverBy::name('username'))->sendKeys('test');
}

帮助解决这个问题！