Fix pick_winner crash on empty lottery pool

src/p2p/peer.py

@@ -90,6 +90,10 @@ async def pick_winner(announcements):
                     if k:
                         for _ in range(k):
                             lottery_pool.append(block["Validator"])
+            if not lottery_pool:
+                # No eligible validator in this round; skip instead of crashing on choice([]).
+                tempblocks.clear()
+                continue
             lottery_winner = choice(lottery_pool)
             print(lottery_winner)
             for block in temp:
@@ -127,4 +131,4 @@ async def run():
     print(Blockchain)
 
     asyncio.ensure_future(candidate(candidate_blocks))
-    asyncio.ensure_future(pick_winner(announcements))
+    asyncio.ensure_future(pick_winner(announcements))

tests/test_pick_winner.py

@@ -0,0 +1,50 @@
+#!/usr/bin/env python3
+
+import asyncio
+
+from p2p import peer
+
+
+def test_pick_winner_ignores_round_without_eligible_validator():
+    async def scenario():
+        original_sleep = peer.asyncio.sleep
+        real_sleep = asyncio.sleep
+        try:
+            async def fast_sleep(_):
+                await real_sleep(0)
+
+            peer.asyncio.sleep = fast_sleep
+            peer.validators.clear()
+            peer.tempblocks.clear()
+            peer.Blockchain.clear()
+            queue = asyncio.Queue()
+            peer.tempblocks.append(
+                {
+                    "Validator": "missing",
+                    "Index": 1,
+                    "BPM": 60,
+                    "Timestamp": "t",
+                    "PrevHash": "h",
+                    "Hash": "h2",
+                }
+            )
+
+            task = asyncio.create_task(peer.pick_winner(queue))
+            for _ in range(100):
+                if peer.tempblocks == []:
+                    break
+                await real_sleep(0.001)
+
+            assert not task.done()
+            assert queue.empty()
+            assert peer.tempblocks == []
+
+            task.cancel()
+            await asyncio.gather(task, return_exceptions=True)
+        finally:
+            peer.asyncio.sleep = original_sleep
+            peer.validators.clear()
+            peer.tempblocks.clear()
+            peer.Blockchain.clear()
+
+    asyncio.run(scenario())