Merge #16079: wallet_balance.py: Prevent edge cases

bb41e632ca wallet_balance.py: Prevent edge cases (Steven Roose)

Pull request description:

  I ran into this edge case when running the test on Elements. I had a 0-value output as change.

ACKs for commit bb41e6:

Tree-SHA512: ef4c25289cafcdb4437f11ed537664dff5afedcefab75a46f985d3be70551de2d3bc8e9cfcb22c0f3d7d2eb95ff40df78b8d01dbacbf90c36bca00426937b0a2

test/functional/wallet_balance.py

@@ -28,12 +28,17 @@ def create_transactions(node, address, amt, fees):
     for utxo in utxos:
         inputs.append({"txid": utxo["txid"], "vout": utxo["vout"]})
         ins_total += utxo['amount']
-        if ins_total + max(fees) > amt:
+        if ins_total >= amt + max(fees):
             break
+    # make sure there was enough utxos
+    assert ins_total >= amt + max(fees)
 
     txs = []
     for fee in fees:
-        outputs = {address: amt, node.getrawchangeaddress(): ins_total - amt - fee}
+        outputs = {address: amt}
+        # prevent 0 change output
+        if ins_total > amt + fee:
+            outputs[node.getrawchangeaddress()] = ins_total - amt - fee
         raw_tx = node.createrawtransaction(inputs, outputs, 0, True)
         raw_tx = node.signrawtransactionwithwallet(raw_tx)
         assert_equal(raw_tx['complete'], True)