test: gettxoutproof duplicate txid

test/functional/rpc_txoutproof.py

@@ -79,6 +79,8 @@ class MerkleBlockTest(BitcoinTestFramework):
         assert_raises_rpc_error(-5, "Not all transactions found in specified or retrieved block", self.nodes[0].gettxoutproof, [txid1, txid3])
         # Test empty list
         assert_raises_rpc_error(-5, "Transaction not yet in block", self.nodes[0].gettxoutproof, [])
+        # Test duplicate txid
+        assert_raises_rpc_error(-8, 'Invalid parameter, duplicated txid', self.nodes[0].gettxoutproof, [txid1, txid1])
 
         # Now we'll try tweaking a proof.
         proof = self.nodes[1].gettxoutproof([txid1, txid2])