Behat 3 - BehatBehatContextStepGiven not found

我第一次用一个简单的例子测试Behat/Mink。当我启动behat时，我出现以下错误：

PHP Fatal error: Class 'Behat'Behat'Context'Step'Given' not found in /var/www/behat-test/features/bootstrap/FeatureContext.php on line 31

features/bootstrap/FeatureContext.php：

<?php
require_once './vendor/autoload.php';
use Behat'Behat'Context'Context;
use Behat'Behat'Context'SnippetAcceptingContext;
use Behat'MinkExtension'Context'MinkContext;
use Behat'Behat'Context'Step;
class FeatureContext extends MinkContext implements Context, SnippetAcceptingContext
{
    // ......
    /**
     * @Given I am logged in as :username
     */
    public function iAmLoggedInAs($username)
    {
        return array(
            new Step'Given('I go to "login.php"'), // line 31
            new Step'When('I fill in "My name" with '.$username),
            new Step'When('I press "Login"')
        );
    }
}