MockHttpRequest request = new MockHttpRequest();
RequestDispatcher rd = deployment.getServletContext().getRequestDispatcher("/aa");
Assert.assertNotNull(rd);
Assert.assertTrue(rd instanceof RequestDispatcherImpl);
RequestDispatcherImpl rdi = (RequestDispatcherImpl) rd;
rdi.mock(request, response);
Assert.assertEquals(HELLO_WORLD, new String(response.out.toByteArray()));
}