Como mokar um método que está marcado com modificador final???

@Test public void responseOk () throws Exception { Chave request = new Chave();

    ResponseService responseMock = mock(ResponseService.class);
    when(responseMock.getResponseBody(Mensagem[].class)).thenReturn(new Mensagem[0]);

    RequestService requestMock = mock(RequestService.class);
    when(requestMock.post("{\"texto\":\"oi\"}")).thenReturn(responseMock);

    ConnectionTemplate  connectionMock = mock(ConnectionTemplate.class);
    when(connectionMock.start()).thenReturn(requestMock); // aqui quando roda lança uma null pointer exception, ppois o método .start() eh final

    Factory factoryMock = Mockito.mock(Factory.class);
    when(factoryMock.getICPConnectionTemplate()).thenReturn(connectionMock);

    controller.setFactory(factoryMock);

    Response response = controller.alteraChave(request);

    assertNotNull(response);
}