[bgp-scale-test] reorder test cases to avoid device unisolation test effect other tests (sonic-net#18256)

What is the motivation for this PR?
The device unisolation test will restart all ports on DUT, after all bgp routes were stable in FRR after ports restart, however, the routes may not stable in ASIC, so the member scale test will be affected.

How did you do it?
To avoid this, move the device unisolation test to the last.

How did you verify/test it?
Run test on DUT

Author: w1nda

tests/bgp/test_ipv6_bgp_scale.py

@@ -347,80 +347,6 @@ def test_sessions_flapping(
         duthost.no_shutdown_multiple(flapping_ports)
 
 
-def test_device_unisolation(
-    duthost,
-    ptfadapter,
-    bgp_peers_info,
-    setup_packet_mask_counters,
-    announce_bgp_routes_teardown
-):
-    '''
-    This test is for the worst senario that all ports are flapped,
-    verify control/data plane have acceptable conergence time.
-    Steps:
-        Shut down all ports on device. (shut down T1 sessions ports on T0 DUT, shut down T0 sesssions ports on T1 DUT.)
-        Wait for routes are stable.
-        Start and keep sending packets with all routes to all portes via ptf.
-        Unshut all ports and wait for routes are stable.
-        Stop sending packets.
-        Estamite control/data plane convergence time.
-    Expected result:
-        Dataplane downtime is less than MAX_DOWNTIME_UNISOLATION.
-    '''
-    pdp = ptfadapter.dataplane
-    exp_mask = setup_packet_mask_counters
-    bgp_ports = [bgp_info[DUT_PORT] for bgp_info in bgp_peers_info.values()]
-    injection_dut_port = random.choice(bgp_ports)
-    injection_port = [i[PTF_PORT] for i in bgp_peers_info.values() if i[DUT_PORT] == injection_dut_port][0]
-    logger.info("Injection port: %s", injection_port)
-
-    startup_routes = get_all_bgp_ipv6_routes(duthost)
-    ecmp_routes = {r: v for r, v in startup_routes.items() if len(v[0]['nexthops']) > 1 and r not in STATIC_ROUTES}
-    pkts = generate_packets(
-        ecmp_routes,
-        duthost.facts['router_mac'],
-        pdp.get_mac(0, injection_port)
-    )
-
-    nexthops_to_remove = [b[IPV6_KEY] for b in bgp_peers_info.values() if b[DUT_PORT] in bgp_ports]
-    expected_routes = remove_nexthops_in_routes(startup_routes, nexthops_to_remove)
-    try:
-        duthost.shutdown_multiple(bgp_ports)
-        ports_shut_time = datetime.datetime.now()
-        recovered = wait_for_ipv6_bgp_routes_recovery(
-            duthost,
-            expected_routes,
-            ports_shut_time,
-            MAX_CONVERGENCE_WAIT_TIME
-        )
-        if not recovered:
-            pytest.fail("BGP routes are not stable in long time")
-    except Exception:
-        duthost.no_shutdown_multiple(bgp_ports)
-
-    terminated = Event()
-    traffic_thread = Thread(
-        target=send_packets, args=(terminated, pdp, 0, injection_port, pkts)
-    )
-    flush_counters(pdp, exp_mask)
-    start_time = datetime.datetime.now()
-    traffic_thread.start()
-    duthost.no_shutdown_multiple(bgp_ports)
-    ports_startup_time = datetime.datetime.now()
-    recovered = wait_for_ipv6_bgp_routes_recovery(
-        duthost,
-        startup_routes,
-        ports_startup_time,
-        MAX_CONVERGENCE_WAIT_TIME
-    )
-    terminated.set()
-    traffic_thread.join()
-    end_time = datetime.datetime.now()
-    validate_rx_tx_counters(pdp, end_time, start_time, exp_mask, MAX_DOWNTIME_UNISOLATION)
-    if not recovered:
-        pytest.fail("BGP routes are not stable in long time")
-
-
 def test_nexthop_group_member_scale(
     duthost,
     ptfadapter,
@@ -515,3 +441,77 @@ def test_nexthop_group_member_scale(
     validate_rx_tx_counters(pdp, end_time, start_time, exp_mask, MAX_DONWTIME_NEXTHOP_GROUP_MEMBER_CHANGE)
     if not recovered:
         pytest.fail("BGP routes are not stable in long time")
+
+
+def test_device_unisolation(
+    duthost,
+    ptfadapter,
+    bgp_peers_info,
+    setup_packet_mask_counters,
+    announce_bgp_routes_teardown
+):
+    '''
+    This test is for the worst senario that all ports are flapped,
+    verify control/data plane have acceptable conergence time.
+    Steps:
+        Shut down all ports on device. (shut down T1 sessions ports on T0 DUT, shut down T0 sesssions ports on T1 DUT.)
+        Wait for routes are stable.
+        Start and keep sending packets with all routes to all portes via ptf.
+        Unshut all ports and wait for routes are stable.
+        Stop sending packets.
+        Estamite control/data plane convergence time.
+    Expected result:
+        Dataplane downtime is less than MAX_DOWNTIME_UNISOLATION.
+    '''
+    pdp = ptfadapter.dataplane
+    exp_mask = setup_packet_mask_counters
+    bgp_ports = [bgp_info[DUT_PORT] for bgp_info in bgp_peers_info.values()]
+    injection_dut_port = random.choice(bgp_ports)
+    injection_port = [i[PTF_PORT] for i in bgp_peers_info.values() if i[DUT_PORT] == injection_dut_port][0]
+    logger.info("Injection port: %s", injection_port)
+
+    startup_routes = get_all_bgp_ipv6_routes(duthost)
+    ecmp_routes = {r: v for r, v in startup_routes.items() if len(v[0]['nexthops']) > 1 and r not in STATIC_ROUTES}
+    pkts = generate_packets(
+        ecmp_routes,
+        duthost.facts['router_mac'],
+        pdp.get_mac(0, injection_port)
+    )
+
+    nexthops_to_remove = [b[IPV6_KEY] for b in bgp_peers_info.values() if b[DUT_PORT] in bgp_ports]
+    expected_routes = remove_nexthops_in_routes(startup_routes, nexthops_to_remove)
+    try:
+        duthost.shutdown_multiple(bgp_ports)
+        ports_shut_time = datetime.datetime.now()
+        recovered = wait_for_ipv6_bgp_routes_recovery(
+            duthost,
+            expected_routes,
+            ports_shut_time,
+            MAX_CONVERGENCE_WAIT_TIME
+        )
+        if not recovered:
+            pytest.fail("BGP routes are not stable in long time")
+    except Exception:
+        duthost.no_shutdown_multiple(bgp_ports)
+
+    terminated = Event()
+    traffic_thread = Thread(
+        target=send_packets, args=(terminated, pdp, 0, injection_port, pkts)
+    )
+    flush_counters(pdp, exp_mask)
+    start_time = datetime.datetime.now()
+    traffic_thread.start()
+    duthost.no_shutdown_multiple(bgp_ports)
+    ports_startup_time = datetime.datetime.now()
+    recovered = wait_for_ipv6_bgp_routes_recovery(
+        duthost,
+        startup_routes,
+        ports_startup_time,
+        MAX_CONVERGENCE_WAIT_TIME
+    )
+    terminated.set()
+    traffic_thread.join()
+    end_time = datetime.datetime.now()
+    validate_rx_tx_counters(pdp, end_time, start_time, exp_mask, MAX_DOWNTIME_UNISOLATION)
+    if not recovered:
+        pytest.fail("BGP routes are not stable in long time")