[test] Integration tests for unbroadcast functionality

Check that...
- mempool tracks & reattempts delivery of a transaction where a GETDATA hasn't
  been requested by a peer yet.
- transaction delivery is not attempted again after GETDATA is received.
- transaction is removed from the unbroadcast set when its removed from the
  mempool.

test/functional/mempool_unbroadcast.py

@@ -0,0 +1,96 @@
+#!/usr/bin/env python3
+# Copyright (c) 2017-2020 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+"""Test that the mempool ensures transaction delivery by periodically sending
+to peers until a GETDATA is received."""
+
+import time
+
+from test_framework.mininode import P2PTxInvStore
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import (
+    assert_equal,
+    connect_nodes,
+    create_confirmed_utxos,
+    disconnect_nodes,
+)
+
+
+class MempoolUnbroadcastTest(BitcoinTestFramework):
+    def set_test_params(self):
+        self.num_nodes = 2
+
+    def skip_test_if_missing_module(self):
+        self.skip_if_no_wallet()
+
+    def run_test(self):
+        self.test_broadcast()
+        self.test_txn_removal()
+
+    def test_broadcast(self):
+        self.log.info("Test that mempool reattempts delivery of locally submitted transaction")
+        node = self.nodes[0]
+
+        min_relay_fee = node.getnetworkinfo()["relayfee"]
+        utxos = create_confirmed_utxos(min_relay_fee, node, 10)
+
+        disconnect_nodes(node, 1)
+
+        self.log.info("Generate transactions that only node 0 knows about")
+
+        # generate a wallet txn
+        addr = node.getnewaddress()
+        wallet_tx_hsh = node.sendtoaddress(addr, 0.0001)
+
+        # generate a txn using sendrawtransaction
+        us0 = utxos.pop()
+        inputs = [{"txid": us0["txid"], "vout": us0["vout"]}]
+        outputs = {addr: 0.0001}
+        tx = node.createrawtransaction(inputs, outputs)
+        node.settxfee(min_relay_fee)
+        txF = node.fundrawtransaction(tx)
+        txFS = node.signrawtransactionwithwallet(txF["hex"])
+        rpc_tx_hsh = node.sendrawtransaction(txFS["hex"])
+
+        # check that second node doesn't have these two txns
+        mempool = self.nodes[1].getrawmempool()
+        assert rpc_tx_hsh not in mempool
+        assert wallet_tx_hsh not in mempool
+
+        self.log.info("Reconnect nodes & check if they are sent to node 1")
+        connect_nodes(node, 1)
+
+        # fast forward into the future & ensure that the second node has the txns
+        node.mockscheduler(15 * 60)  # 15 min in seconds
+        self.sync_mempools(timeout=30)
+        mempool = self.nodes[1].getrawmempool()
+        assert rpc_tx_hsh in mempool
+        assert wallet_tx_hsh in mempool
+
+        self.log.info("Add another connection & ensure transactions aren't broadcast again")
+
+        conn = node.add_p2p_connection(P2PTxInvStore())
+        node.mockscheduler(15 * 60)
+        time.sleep(5)
+        assert_equal(len(conn.get_invs()), 0)
+
+    def test_txn_removal(self):
+        self.log.info("Test that transactions removed from mempool are removed from unbroadcast set")
+        node = self.nodes[0]
+        disconnect_nodes(node, 1)
+        node.disconnect_p2ps
+
+        # since the node doesn't have any connections, it will not receive
+        # any GETDATAs & thus the transaction will remain in the unbroadcast set.
+        addr = node.getnewaddress()
+        txhsh = node.sendtoaddress(addr, 0.0001)
+
+        # check transaction was removed from unbroadcast set due to presence in
+        # a block
+        removal_reason = "Removed {} from set of unbroadcast txns before confirmation that txn was sent out".format(txhsh)
+        with node.assert_debug_log([removal_reason]):
+            node.generate(1)
+
+if __name__ == "__main__":
+    MempoolUnbroadcastTest().main()

test/functional/test_runner.py

@@ -207,6 +207,7 @@ BASE_SCRIPTS = [
     'p2p_unrequested_blocks.py',
     'feature_includeconf.py',
     'feature_asmap.py',
+    'mempool_unbroadcast.py',
     'rpc_deriveaddresses.py',
     'rpc_deriveaddresses.py --usecli',
     'rpc_scantxoutset.py',