public function testGetTimestamp()
 {
     $this->adapter->write('dummy.txt', '1234', new Config());
     $result = $this->adapter->getTimestamp('dummy.txt');
     $this->assertInternalType('array', $result);
     $this->assertArrayHasKey('timestamp', $result);
     $this->assertInternalType('int', $result['timestamp']);
 }