Use MockWebServer to test your app under SocketIO fail.

SocketIOTest.java

    @Test
    public void testDemoResponseErrorSocket() {
        reset(mainSceneMock);

        MainPresenterImpl presenter = new MainPresenterImpl(schedulersProvider, pokemonService);

        MockResponse response = new MockResponse();
        response.setBody("\"message\":\"Hello\"").throttleBody(1, 2, TimeUnit.SECONDS);

        getErrorMockWebServer().enqueue(response);

        presenter.onSceneAdded(mainSceneMock, null);

        testScheduler.triggerActions();

        verify(mainSceneMock, times(1)).showErrorDialog(anyString());
        verify(mainSceneMock, times(0)).setApiText(anyString());
    }