Ruby spec a ffi-rzmq project

Intro

When working with async messaging, tests are more difficult. ffi-rzmq library is special because messages are received in a weird way:

receiver.recv_string(buffer = "")

The message payload is in the buffer variable, which is passed as a parameter. To achieve testing I had to turn buffer to a instance variable (@buffer) and I resorted to the mock results Arbitrary Handling

    # e is a Emitter instance, my fictionary zeromq-based class
    @endpoint.should_receive(:recv_string) do
      e.instance_variable_set("@buffer", my_data)
    end
    @endpoint.should_receive(:recv_string) do 
      e.instance_variable_set("@buffer", "__END_OF_DATA__")
    end

@endpoint is a mocked socket: when it receives the recv_string method, it replaces @buffer instance variable on e. Please have a look at the example code.