Merge bitcoin/bitcoin#30264: test: add coverage for errors for combinerawtransaction

ab98e6f test: add coverage for errors for `combinerawtransaction` RPC (brunoerg)

Pull request description:

  This PR adds test coverage for the following errors for the `combinerawtransaction` RPC:

  * Tx decode failed
  * Missing transactions
  * Input not found or already spent

  For reference: https://maflcko.github.io/b-c-cov/total.coverage/src/rpc/rawtransaction.cpp.gcov.html

ACKs for top commit:
  maflcko:
    lgtm ACK ab98e6f
  tdb3:
    ACK ab98e6f

Tree-SHA512: 8a133c25dad2e1b236e0278a88796f60f763e3fd6fbbc080f926bb23f9dcc55599aa242d6e0c4ec15a179d9ded10a1f17ee5b6063719107ea84e6099f10416b2

Author: fanquake

test/functional/rpc_rawtransaction.py

@@ -585,13 +585,16 @@ def raw_multisig_transaction_legacy_tests(self):
         rawTxPartialSigned2 = self.nodes[2].signrawtransactionwithwallet(rawTx2, inputs)
         self.log.debug(rawTxPartialSigned2)
         assert_equal(rawTxPartialSigned2['complete'], False)  # node2 only has one key, can't comp. sign the tx
+        assert_raises_rpc_error(-22, "TX decode failed", self.nodes[0].combinerawtransaction, [rawTxPartialSigned1['hex'], rawTxPartialSigned2['hex'] + "00"])
+        assert_raises_rpc_error(-22, "Missing transactions", self.nodes[0].combinerawtransaction, [])
         rawTxComb = self.nodes[2].combinerawtransaction([rawTxPartialSigned1['hex'], rawTxPartialSigned2['hex']])
         self.log.debug(rawTxComb)
         self.nodes[2].sendrawtransaction(rawTxComb)
         rawTx2 = self.nodes[0].decoderawtransaction(rawTxComb)
         self.sync_all()
         self.generate(self.nodes[0], 1)
         assert_equal(self.nodes[0].getbalance(), bal + Decimal('50.00000000') + Decimal('2.19000000'))  # block reward + tx
+        assert_raises_rpc_error(-25, "Input not found or already spent", self.nodes[0].combinerawtransaction, [rawTxPartialSigned1['hex'], rawTxPartialSigned2['hex']])
 
 
 if __name__ == '__main__':