Support CI DbTest

```php
class TestDb_Demo extends \CI_DbTestCase {  
                                                                                                                                                                                                                                                                                                          
    public function getDataSet()                                                                                           
    {       
        //load default data                                                                                              
        return new \PHPUnit_Extensions_Database_DataSet_YamlDataSet(                                                       
            fixture('user.yml')                                                                                            
        );                                                                                                                 
    }                                                                                                                      
                                                                                                                           
    public function testUserCount()                                                                                        
    {      
        //@todo User::add($params);    
        //assert table users increase 1                                                                                           
        $this->assertEquals(2, $this->getConnection()->getRowCount('users'));                                              
    }                                                                                                                                                                                                                            
}   
```