Callback::check(123, syntax: true), Nette\InvalidArgumentException::class, 'Given value is not a callable type.', ); Assert::exception( fn() => Callback::check('undefined'), Nette\InvalidArgumentException::class, "Callback 'undefined' is not callable.", ); // PHP bugs - is_callable($object, true) fails Assert::exception( fn() => Callback::check(new stdClass), Nette\InvalidArgumentException::class, "Callback 'stdClass::__invoke' is not callable.", ); Assert::exception( fn() => Callback::check(new stdClass, syntax: true), Nette\InvalidArgumentException::class, 'Given value is not a callable type.', );