PCU: introduce TC_egprs_pkt_chan_req_reject_exhaustion

Send 7 RACH indications to the IUT with EGPRS Packet Channel Request.
Since we have only one timeslot (and USF value '111'B is reserved),
the 8-th indication should be properly rejected by the IUT.

Change-Id: Ie6e5fc68e1591c57e21541ba16fbdcd3fe477ac7
Related: OS#1548
diff --git a/pcu/PCU_Tests.ttcn b/pcu/PCU_Tests.ttcn
index 999ece0..8a1a425 100644
--- a/pcu/PCU_Tests.ttcn
+++ b/pcu/PCU_Tests.ttcn
@@ -1861,6 +1861,39 @@
 	f_shutdown(__BFILE__, __LINE__, final := true);
 }
 
+/* Make sure that IUT responds with RR Immediate Assignment Reject due to exhaustion. */
+testcase TC_egprs_pkt_chan_req_reject_exhaustion() runs on RAW_PCU_Test_CT {
+	var template IARRestOctets rest;
+	var BIT11 ra11;
+
+	/* Initialize the PCU interface abstraction */
+	f_init_raw(testcasename());
+
+	var EGPRSPktChRequest req := {
+		one_phase := {
+			tag := '0'B,
+			multislot_class := '10101'B,
+			priority := '01'B,
+			random_bits := '101'B
+		}
+	};
+
+	/* We send 7 requests, the IUT gives us all available USFs (0..6).
+	 * TODO: make it configurable: usf_max := mp_pdch_ts_num * 7. */
+	for (var integer i := 0; i < 7; i := i + 1) {
+		req.one_phase.random_bits := int2bit(f_rnd_int(8), 3);
+		f_TC_egprs_pkt_chan_req(req, tr_IMM_TBF_ASS);
+	}
+
+	ra11 := enc_EGPRSPktChRequest2bits(req);
+	rest := tr_IARRestOctets({ *, tr_ExtRAOpt(substr(ra11, 6, 5)), * });
+
+	/* At this point, the IUT should run out of free USFs */
+	f_TC_egprs_pkt_chan_req_reject(ra11, 1870, rest);
+
+	f_shutdown(__BFILE__, __LINE__, final := true);
+}
+
 control {
 	execute( TC_pcuif_suspend() );
 	execute( TC_ta_ptcch_idle() );
@@ -1895,6 +1928,7 @@
 	execute( TC_egprs_pkt_chan_req_two_phase() );
 	execute( TC_egprs_pkt_chan_req_reject_content() );
 	execute( TC_egprs_pkt_chan_req_reject_emergency() );
+	execute( TC_egprs_pkt_chan_req_reject_exhaustion() );
 
 	execute( TC_mo_ping_pong_with_ul_racap_egprs_only() );
 }