Testing REST calls and connection

I want to use Robolectric to unit test my application, but I don't really understand how can I test in my application. It has only one button that start the method connect(). This method calls sequentially 4 HTTP call, everyone with the result of the previous as body (more or less). So, i have asynctask to do POST request and in postExtecute I call the next POST.

connect -> Call A -> Call B with some A data like auth token -> Call C with b data -> call D with C data.

how can I test It? I don't have the server UP, so basically I use roboeletric Fake HTTP Layer to simulate response.