test_scheduler: Skip next check after reached done state

Two RID would change status at the same time when one of
them entering done state (prepare_done and run_done).
So once any of them enter that state, checking in next
notify would be skipped.

artiq/test/test_scheduler.py

@@ -148,17 +148,41 @@ def test_pending_priority(self):
         done = asyncio.Event()
 
         schedule = {}
-        pending_to_preparing = []
+
+        expect = [
+            {0: "pending"},
+            {0: "pending", 1: "pending"},
+            {0: "pending", 1: "pending", 2: "pending"},
+            {0: "preparing", 1: "pending", 2: "pending"},
+            {0: "running", 1: "pending", 2: "preparing"},
+            {0: "paused", 1: "pending", 2: "running"},
+            {0: "running", 1: "pending", 2: "analyzing"},
+            {0: "running", 1: "pending", 2: "deleting"},
+        ]
+        expect_idx = 0
+        skip_next = False
 
         def notify(mod):
+            nonlocal expect_idx, skip_next
             process_mod(schedule, mod)
-            for key in schedule:
-                if schedule[key]["status"] == "preparing":
-                    if key not in pending_to_preparing:
-                        pending_to_preparing.append(key)
-            # Expect only two rid would go to preparing
-            if len(pending_to_preparing) == 2:
-                self.assertEqual(pending_to_preparing, [0, 2])
+
+            # gather status of each RID
+            current_status = {}
+            for rid, info in schedule.items():
+                current_status[rid] = info["status"]
+
+            # ignore intermediate state
+            if skip_next:
+                skip_next = False
+            else:
+                if "prepare_done" not in current_status.values() and\
+                    "run_done" not in current_status.values():
+                        self.assertEqual(current_status, expect[expect_idx])
+                        expect_idx += 1
+                else:
+                    skip_next = True
+
+            if expect_idx >= len(expect):
                 done.set()
 
         scheduler.notifier.publish = notify