public function testCache()
 {
     $cacheKeys = array('block_id' => '1');
     $cache = new CacheElement($cacheKeys, 'data', 20);
     $this->assertEquals(20, $cache->getTtl());
     $this->assertEquals($cacheKeys, $cache->getKeys());
     $this->assertFalse($cache->isExpired());
     $cache = new CacheElement($cacheKeys, 'data', -1);
     $this->assertTrue($cache->isExpired());
     $this->assertEquals('data', $cache->getData());
     $cache->getExpirationDate();
 }