Testcase for wallet issue with orphaned rewards.

This adds a new test case demonstrating the wallet issue when block
rewards are orphaned (bitcoin#14148).

test/functional/test_runner.py

@@ -224,6 +224,7 @@
     'rpc_deriveaddresses.py --usecli',
     'rpc_scantxoutset.py',
     'feature_logging.py',
+    'wallet_orphanedreward.py',
     'p2p_node_network_limited.py',
     'p2p_permissions.py',
     'feature_blocksdir.py',

test/functional/wallet_orphanedreward.py

@@ -0,0 +1,54 @@
+#!/usr/bin/env python3
+# Copyright (c) 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 orphaned block rewards in the wallet."""
+
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import assert_equal, assert_raises_rpc_error
+
+
+class OrphanedBlockRewardTest(BitcoinTestFramework):
+    def set_test_params(self):
+        self.setup_clean_chain = True
+        self.num_nodes = 2
+        self.supports_cli = False
+
+    def skip_test_if_missing_module(self):
+        self.skip_if_no_wallet()
+
+    def run_test(self):
+        # Generate some blocks and obtain some coins on node 0.  We send
+        # some balance to node 1, which will hold it as a single coin.
+        self.nodes[0].generate (150)
+        self.nodes[0].sendtoaddress (self.nodes[1].getnewaddress (), 10)
+        self.nodes[0].generate (50)
+
+        # Get a block reward with node 1 and remember the block so we can orphan
+        # it later.
+        self.sync_blocks ()
+        blk = self.nodes[1].generate (1)[0]
+        self.sync_blocks ()
+
+        # Let the block reward mature and send coins including both
+        # the existing balance and the block reward.
+        self.nodes[0].generate (150)
+        assert_equal (self.nodes[1].getbalance (), 10 + 25)
+        txid = self.nodes[1].sendtoaddress (self.nodes[0].getnewaddress (), 30)
+
+        # Orphan the block reward and observe that also the original coins
+        # from the wallet are still locked.
+        self.nodes[0].invalidateblock (blk)
+        self.nodes[0].generate (200)
+        self.sync_blocks ()
+        assert_raises_rpc_error (-6, 'Insufficient funds',
+                                 self.nodes[1].sendtoaddress,
+                                 self.nodes[0].getnewaddress (), 9)
+
+        # Abandoning the transaction frees the funds again.
+        self.nodes[1].abandontransaction (txid)
+        self.nodes[1].sendtoaddress (self.nodes[0].getnewaddress (), 9)
+
+
+if __name__ == '__main__':
+    OrphanedBlockRewardTest().main()