public function testAverage()
 {
     $this->mockEngineMethod('average')->with($this->equalTo('table'), $this->equalTo('column'), $this->equalTo('where'), $this->equalTo(['param']))->will($this->returnValue(true));
     $this->assertTrue(DbClient::average("table", 'column', 'where', ['param']));
 }
 /**
  * @param string $columnName
  * @param array|string $where
  * @param array $params
  * @return mixed
  */
 public static function average($columnName, $where = null, $params = null)
 {
     return DbClient::average(static::getTableName(), $columnName, $where, $params);
 }