Adding new route to test client in Symfony

I am trying to add new route in test case extending Symfony\Bundle\FrameworkBundle\Test\KernelTestCase that will throw exception, to test EventListener for it. Simplified tests will looks like this:

public function testHandlingException()
{
    $kernel = $this->createKernel(['environment' => 'test', 'debug' => true]);
    $kernel->boot();

    $client = $kernel->getContainer()->get('test.client');

    $controller = new class extends Controller {
        public function testAction()
        {
            throw new \Exception();
        }
    };

    $route = new Route(
        'route_500',
        ['_controller' => get_class($controller).'::testAction']
    );

    $client
        ->getContainer()
        ->get('router')
        ->getRouteCollection()
        ->add('route_500', $route);

    $this->expectException(\Exception::class);

    $client->request('GET', '/route_500');
}

It fails with:

Failed asserting that exception of type "Exception" is thrown.

How can I add route in-fly so calling it will work?