how to test if variables exists in function with phpunit

I am writing Unit-Tests for a Class looking like this:

class example {

    public function __construct($param1, $param2) {
        $this->param1 = $param1
        $this->param2 = $param2
    }
}

Is it possible to test if $this->param1 and $this->param2 exists after the constructor is executed? I already googled for this but didn't found a valid answer to this. I tried it with the Assertion contain, but this didn't work too.