test: test decodepsbt fee calculation (count input value only once per UTXO)

Checks that the RPC decodepsbt calculates the fee correctly, in particular for
PSBTs with segwit inputs that have both a witness- and a non-witness-UTXO type
set. Before commit 7512278 ("Increment input
value sum only once per UTXO in decodepsbt") the values for those inputs were
double counted.

Author: theStack

test/functional/rpc_psbt.py

@@ -155,12 +155,14 @@ def run_test(self):
                 p2pkh_pos = out['n']
 
         # spend single key from node 1
-        rawtx = self.nodes[1].walletcreatefundedpsbt([{"txid":txid,"vout":p2wpkh_pos},{"txid":txid,"vout":p2sh_p2wpkh_pos},{"txid":txid,"vout":p2pkh_pos}], {self.nodes[1].getnewaddress():29.99})['psbt']
-        walletprocesspsbt_out = self.nodes[1].walletprocesspsbt(rawtx)
+        created_psbt = self.nodes[1].walletcreatefundedpsbt([{"txid":txid,"vout":p2wpkh_pos},{"txid":txid,"vout":p2sh_p2wpkh_pos},{"txid":txid,"vout":p2pkh_pos}], {self.nodes[1].getnewaddress():29.99})
+        walletprocesspsbt_out = self.nodes[1].walletprocesspsbt(created_psbt['psbt'])
         # Make sure it has both types of UTXOs
         decoded = self.nodes[1].decodepsbt(walletprocesspsbt_out['psbt'])
         assert 'non_witness_utxo' in decoded['inputs'][0]
         assert 'witness_utxo' in decoded['inputs'][0]
+        # Check decodepsbt fee calculation (input values shall only be counted once per UTXO)
+        assert_equal(decoded['fee'], created_psbt['fee'])
         assert_equal(walletprocesspsbt_out['complete'], True)
         self.nodes[1].sendrawtransaction(self.nodes[1].finalizepsbt(walletprocesspsbt_out['psbt'])['hex'])