public function testPrePersist()
 {
     $this->assertNull($this->entity->getCreatedAt());
     $this->entity->prePersist();
     $result = $this->entity->getCreatedAt();
     $this->assertInstanceOf('DateTime', $result);
     $this->assertLessThan(3, $result->diff(new \DateTime())->s);
     $this->entity->prePersist();
     $this->assertSame($result, $this->entity->getCreatedAt());
 }