Test cases to test a function phpunit

I'm new to php unit testing, What are the valid test cases for below function.

 protected function validateParams($graph, $start, $destination)
{
    if (!is_object($graph)) {

        throw new \InvalidArgumentException('Graph param should be an object !');
    }

    if (empty($start)) {

        throw new \InvalidArgumentException('Start param is empty !');
    }

    if (empty($destination)) {

        throw new \InvalidArgumentException('Graph param is empty !');
    }

    return true;
}