private void testSetSocketImpl(HttpServletResponse response)
    throws IOException, AssertionFailedException {
  SocketImplFactory mockFactory =
      new SocketImplFactory() {
        @Override
        public SocketImpl createSocketImpl() {
          return null;
        }
      };

  SocketException caught = null;
  try {
    Socket.setSocketImplFactory(mockFactory);
  } catch (SocketException e) {
    caught = e;
  }
  assertNotNull("caught", caught, response);
}