[doc] A bit more doc about the DCS mock setup

Author: knopers8

core/integration/README.md

@@ -29,6 +29,7 @@ CCDB plugin calls PDP-provided executable which creates a General Run Parameters
 ## DCS
 
 DCS plugin communicates with the ALICE Detector Control System (DCS).
+In particular, it communicates with a gRPC endpoint exposed by `ecs2dcsgateway` (developed by the DCS team), which then passes the requests to the DCS.
 
 ### DCS operations
 
@@ -151,6 +152,23 @@ From the AliECS user point of view, state sequences can be defined as the follow
 - `dcs_sor_state_sequence`
 - `dcs_eor_state_sequence`
 
+#### Testing tips
+
+Typical valid sequences are:
+
+```
+{
+  "dcs_pfr_state_sequence": "1000:RUN_OK",
+  "dcs_sor_state_sequence": "1000:SOR_PROGRESSING,3000:RUN_OK",
+  "dcs_eor_state_sequence": "1000:EOR_PROGRESSING,3000:RUN_OK"
+}
+```
+
+`PFR_AVAILABLE` and `SOR_AVAILABLE` are typically send by DCS via the heartbeat stream, so requesting them as an answer to an operation request does not reflect the behaviour of the production system.
+
+To trigger a `TIMEOUT` event, one should not request a `TIMEOUT` state in the sequence, but rather put a too long delay compared to the provided gRPC timeout.
+Both in the production and the mock setup, `TIMEOUT` events are generated by `ecs2dcsgateway` when a detector does not respond to a request within the specified timeout.
+
 ## DD Scheduler
 
 DD scheduler plugin informs the Data Distribution software about the pool of FLPs taking part in data taking.