[qa] zapwallettxes: Wait up to 3s for mempool reload

Github-Pull: #11308
Rebased-From: fadd0c16b6

test/functional/zapwallettxes.py

@@ -15,8 +15,10 @@
   been zapped.
 """
 from test_framework.test_framework import BitcoinTestFramework
-from test_framework.util import (assert_equal,
+from test_framework.util import (
+    assert_equal,
     assert_raises_jsonrpc,
+    wait_until,
 )
 
 class ZapWalletTXesTest (BitcoinTestFramework):
@@ -56,6 +58,8 @@ class ZapWalletTXesTest (BitcoinTestFramework):
         self.stop_node(0)
         self.start_node(0, ["-persistmempool=1", "-zapwallettxes=2"])
 
+        wait_until(lambda: self.nodes[0].getmempoolinfo()['size'] == 1, timeout=3)
+
         assert_equal(self.nodes[0].gettransaction(txid1)['txid'], txid1)
         assert_equal(self.nodes[0].gettransaction(txid2)['txid'], txid2)