PHP7 type hinting not causing warnings in PHPStorm

I've created a test class to test type hinting. The code obviously fails, but PHPStorm does not detect the error. I wanted to test if PHPStorm could warn me against these kind of errors. Is this not implemented, a bug, or have I missed a setting?

<?php
declare(strict_types=1);

class Test
{

    /**
     * Test constructor.
     * @param int $x
     * @return int
     */
    public function test(int $x) : int
    {
        unset($x);
        return '';
    }

    public function test2()
    {
        return $this->test('');
    }


}

$t = new Test();

echo $t->Test();