如何在PHPUnit中测试STDIN

class Reader 
{
    const STREAM_READ = 'php://stdin';

    private $_streamHandle;

    public function __construct($stream = self::STREAM_READ)
    {
        $this->_streamHandle = fopen($stream,'r');
    }

    public function getReadedValue()
    {
        $value = trim(fgets($this->_streamHandle));

        return $value;
    }

    public function __destruct()
    {
        fclose($this->_streamHandle);
    }
}

现在是我的问题,我如何测试这个类,从stdin读取一些东西并通过getReadedValue()函数返回readed值？