我如何访问变量按钮:包含类css phpUnit symfony2

 <button class="btn btn-lg btn-yellow" type="submit" ng-click="submitForm($event)">
<span class="visible-xs glyphicon glyphicon-search"> </span>
<span class="hidden-xs">Rechercher</span>
</button>

类:问题:$crawler->selectButton('。BTN BTN - lgbtn -yellow')不存在如何访问这个变量?因为我没有Id或name

  private $client;
protected function setUp()
{
    $client = static::createClient();
    $this->client = $client;
}

    public function testForm()
{
    $crawler = $this->client->request('GET', '/test');
    $form = $crawler->selectButton('.btn btn-lg btn-yellow')->form();
    $form->setValues(
        array(
            'form[search[searchName]]' => 'nom',
            //'form[search]' => 'search'
        )
    );
    $this->client->submit($form);