Elastica\Connection\Strategy\CallbackStrategy::isValid PHP Method

    public static function isValid($callback)
    {
        return is_callable($callback);
    }

 /**
  * @group unit
  */
 public function testFailIsValid()
 {
     $isValid = CallbackStrategy::isValid(new \stdClass());
     $this->assertFalse($isValid);
     $isValid = CallbackStrategy::isValid('array_pop_pop_pop_pop_pop_pop');
     $this->assertFalse($isValid);
 }