tests: Improve p2p tx propagation functional test

Reduce the likelihood of false positive failures in the p2p
transaction propagation functional test by waiting up to a
maximum timeout for a transaction to propagate, rather than using a
fixed timeout, to reflect the random delay of Dandelion++ transaction
propagation. This strategy also speeds test execution in cases where
propagation occurs faster than the previously expected fixed delay.

tests/functional_tests/p2p.py

@@ -160,12 +160,11 @@ def test_p2p_reorg(self):
 
     def test_p2p_tx_propagation(self):
         print('Testing P2P tx propagation')
-        daemon2 = Daemon(idx = 2)
-        daemon3 = Daemon(idx = 3)
+        daemons = (Daemon(idx = 2), Daemon(idx = 3))
 
-        for daemon in [daemon2, daemon3]:
+        for daemon in daemons:
             res = daemon.get_transaction_pool_hashes()
-            assert not 'tx_hashes' in res or len(res.tx_hashes) == 0
+            assert len(res.get('tx_hashes', [])) == 0
 
         self.wallet.refresh()
         res = self.wallet.get_balance()
@@ -175,12 +174,29 @@ def test_p2p_tx_propagation(self):
         assert len(res.tx_hash) == 32*2
         txid = res.tx_hash
 
-        time.sleep(5)
-
-        for daemon in [daemon2, daemon3]:
-            res = daemon.get_transaction_pool_hashes()
-            assert len(res.tx_hashes) == 1
-            assert res.tx_hashes[0] == txid
+        # Due to Dandelion++, the network propagates transactions with a
+        # random delay, so poll for the transaction with a timeout
+        timeout = 16
+        pending_daemons = set(daemons)
+        expected_hashes = [txid]
+        wait_cutoff = time.monotonic() + timeout
+        while True:
+            done = []
+            for daemon in pending_daemons:
+                res = daemon.get_transaction_pool_hashes()
+                hashes = res.get('tx_hashes')
+                if hashes:
+                    assert hashes == expected_hashes
+                    done.append(daemon)
+            pending_daemons.difference_update(done)
+            if len(pending_daemons) == 0:
+                break
+            max_delay = wait_cutoff - time.monotonic()
+            if max_delay <= 0:
+                break
+            time.sleep(min(.25, max_delay))
+        npending = len(pending_daemons)
+        assert npending == 0, '%d daemons pending' % npending
 
 
 if __name__ == '__main__':