Update happy path rx/tx fdm test to read and write data from the call…

…back

tests/test_fdm_connection.py

@@ -39,8 +39,12 @@ def mock_socket_bind(self, addr):
 
 
 @pytest.mark.parametrize('fdm_version', supported_fdm_versions)
-def test_fdm_happypath(mocker, fdm_version):
-    rx_cb = lambda s, e_p: s
+def test_fdm_rx_and_tx(mocker, fdm_version):
+    def rx_cb(fdm_data, event_pipe):
+        run_idx, = event_pipe.child_recv()
+        callback_version = fdm_data['version']
+        event_pipe.child_send((run_idx, callback_version,))
+        return fdm_data
 
     fdm_c = FDMConnection(fdm_version)
 
@@ -49,6 +53,10 @@ def test_fdm_happypath(mocker, fdm_version):
     fdm_c.connect_rx('localhost', 55550, rx_cb)
     fdm_c.connect_tx('localhost', 55551)
 
-    for i in range(500):
+    for i in range(100):
+        fdm_c.event_pipe.parent_send((i,))
         # manually call the process instead of having the process spawn
         fdm_c._fg_packet_roundtrip()
+        run_idx, callback_version = fdm_c.event_pipe.parent_recv()
+        assert run_idx == i
+        assert callback_version == fdm_version