symfony4-phpunit-InvalidArgumentException：无法访问的字段“”

Question

我正在尝试在symfony 4中运行几个单元测试。实际上，我正在尝试测试表单提交。

这是我的单元测试，

public function testAccountCreation() {
        $this->logIn();
        $crawler = $this->client->request('GET', '/admin/account');
        $form = $crawler->selectButton('admin_user[save]')->form();

        $form['admin_user[displayName]'] = 'Vim';
        $form['admin_user[username]'] = 'user5@user.com';
        $form['admin_user[password]'] = 'P3ssword';
        $form['admin_user[phoneNumber]'] = '1234789';
        $form['admin_user[roles][]'] = 'ROLE_ADMIN';

        $crawler = $this->client->submit($form);
        $this->assertContains(
                'Your changes were saved!', $this->client->getResponse()->getContent()
        );
}

但是我遇到这个错误，

  

App \ Tests \ AdminControllerTest :: testAccountCreation   InvalidArgumentException：无法访问的字段“”

如果有人可以帮助，那就太好了。