[test] fundrawtransaction: lock watch-only shared address

self.nodes[0] creates an address which is watch-only-shared with self.nodes[3]. If nodes[0] spends the associated UTXO during any of its sends later, the watchonly test will fail, as nodes[3] now has insufficient funds.

Note that this also adds a new find_vout_for_address function to the test framework.

test/functional/rpc_fundrawtransaction.py

@@ -4,8 +4,18 @@
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 """Test the fundrawtransaction RPC."""
 
+from decimal import Decimal
 from test_framework.test_framework import BitcoinTestFramework
-from test_framework.util import *
+from test_framework.util import (
+    assert_equal,
+    assert_fee_amount,
+    assert_greater_than,
+    assert_greater_than_or_equal,
+    assert_raises_rpc_error,
+    connect_nodes_bi,
+    count_bytes,
+    find_vout_for_address,
+)
 
 
 def get_unspent(listunspent, amount):
@@ -57,6 +67,11 @@ class RawTransactionsTest(BitcoinTestFramework):
         watchonly_amount = Decimal(200)
         self.nodes[3].importpubkey(watchonly_pubkey, "", True)
         watchonly_txid = self.nodes[0].sendtoaddress(watchonly_address, watchonly_amount)
+
+        # Lock UTXO so nodes[0] doesn't accidentally spend it
+        watchonly_vout = find_vout_for_address(self.nodes[0], watchonly_txid, watchonly_address)
+        self.nodes[0].lockunspent(False, [{"txid": watchonly_txid, "vout": watchonly_vout}])
+
         self.nodes[0].sendtoaddress(self.nodes[3].getnewaddress(), watchonly_amount / 10)
 
         self.nodes[0].sendtoaddress(self.nodes[2].getnewaddress(), 1.5)
@@ -472,6 +487,9 @@ class RawTransactionsTest(BitcoinTestFramework):
         connect_nodes_bi(self.nodes,1,2)
         connect_nodes_bi(self.nodes,0,2)
         connect_nodes_bi(self.nodes,0,3)
+        # Again lock the watchonly UTXO or nodes[0] may spend it, because
+        # lockunspent is memory-only and thus lost on restart
+        self.nodes[0].lockunspent(False, [{"txid": watchonly_txid, "vout": watchonly_vout}])
         self.sync_all()
 
         # drain the keypool

test/functional/test_framework/util.py

@@ -569,3 +569,14 @@ def mine_large_block(node, utxos=None):
     fee = 100 * node.getnetworkinfo()["relayfee"]
     create_lots_of_big_transactions(node, txouts, utxos, num, fee=fee)
     node.generate(1)
+
+def find_vout_for_address(node, txid, addr):
+    """
+    Locate the vout index of the given transaction sending to the
+    given address. Raises runtime error exception if not found.
+    """
+    tx = node.getrawtransaction(txid, True)
+    for i in range(len(tx["vout"])):
+        if any([addr == a for a in tx["vout"][i]["scriptPubKey"]["addresses"]]):
+            return i
+    raise RuntimeError("Vout not found for address: txid=%s, addr=%s" % (txid, addr))