mock:模拟公开覆盖的受保护方法

我有一个带有抽象保护方法的抽象基类

abstract class AbstractSample
{
    abstract protected function getConnection();
}

和子类，其中protected方法被重定义为public:

class ConcreteSample extends AbstractSample
{
    public function getConnection()
    {
        return 'connection resource';
    }
}

这是我要测试的类:

class Caller
{
    protected $_sample;
    public function __construct(ConcreteSample $sample)
    {
        $this->_sample = $sample;
    }
    public function method()
    {
        $conn = $this->_sample->getConnection();
        return $conn;
    }
}

和测试单元本身:

class Sample_Test extends 'PHPUnit_Framework_TestCase
{
    public function test_getConnection()
    {
        $RESOURCE = 'mocked resource';
        $mSample = 'Mockery::mock(ConcreteSample::class);
        $mSample
            ->shouldReceive('getConnection')->once()
            ->andReturn($RESOURCE);
        $obj = new Caller($mSample);
        $res = $obj->method();
        $this->assertEquals($RESOURCE, $res);
    }
}

当我运行测试时，我有一个错误:

InvalidArgumentException : getConnection() cannot be mocked as it a protected method and mocking protected methods is not allowed for this mock
 /.../vendor/mockery/mockery/library/Mockery.php:670
 /.../vendor/mockery/mockery/library/Mockery.php:678
 /.../vendor/mockery/mockery/library/Mockery.php:629
 /.../var/tmp/Sample_Test.php:13

如何模拟在基类中重新定义受保护方法的公共方法?嘲弄版本为0.9.4