Kahlan\Plugin\Stub::__construct PHP Method

    public function __construct($reference)
    {
        $reference = $this->_reference($reference);
        $isString = is_string($reference);
        if ($isString) {
            if (!class_exists($reference)) {
                throw new InvalidArgumentException("Can't Stub the unexisting class `{$reference}`.");
            }
            $reference = ltrim($reference, '\\');
            $reflection = Inspector::inspect($reference);
        } else {
            $reflection = Inspector::inspect(get_class($reference));
        }
        if (!$reflection->isInternal()) {
            $this->_reference = $reference;
            return;
        }
        if (!$isString) {
            throw new InvalidArgumentException("Can't Stub built-in PHP instances, create a test double using `Double::instance()`.");
        }
        $this->_needToBePatched = true;
        return $this->_reference = $reference;
    }