PHP Reflection class newInstance exit on execution

I'm writing controller testing unit with Fuelphp framework. And inside the code I'm trying to request application controller like this one :

$response = Request::force('controller_name/controller_method')->set_method('GET')->execute();

But this code unexpectedly exits the entire testing unit like PHP exit function. After trying to figure out what happened inside the core source code, I found out that in line 440 of https://github.com/fuel/core/blob/1.9/develop/classes/request.php forces the program to exit without any exception.

$this->controller_instance = $class->newInstance($this);

And before this code

$class = new \ReflectionClass($this->controller)

I'm using PHP 5.6.33 and Fuelphp 1.7.2 in my machine and I hope someone can help me with this error.