Merge bitcoin/bitcoin#31943: test: add coverage for abandoning unconfirmed transaction

073a017 test: add coverage for abandoning unconfirmed transaction (rkrux)

Pull request description:

  Previous discussion: bitcoin/bitcoin#31794 (review)
  Current Coverage: https://maflcko.github.io/b-c-cov/total.coverage/src/wallet/wallet.cpp.gcov.html#L1326

ACKs for top commit:
  Eunovo:
    Tested ACK bitcoin/bitcoin@073a017
  janb84:
    Tested ACK [073a017](bitcoin/bitcoin@073a017)
  maflcko:
    lgtm ACK 073a017
  Prabhat1308:
    Concept ACK [`073a017`](bitcoin/bitcoin@073a017)
  brunoerg:
    utACK 073a017

Tree-SHA512: be9b3d2e1cf65b20369be44d333aa2244b3af588f4a90374ad9562c3ea336669ba8f98a5fb88d616ba1f1f1b7dc0ad9bb47e7167aa03a52f2e0601525e156345

Author: fanquake

test/functional/wallet_abandonconflict.py

@@ -45,6 +45,10 @@ def run_test(self):
         txB = alice.sendtoaddress(alice.getnewaddress(), Decimal("10"))
         txC = alice.sendtoaddress(alice.getnewaddress(), Decimal("10"))
         self.sync_mempools()
+
+        # Can not abandon transaction in mempool
+        assert_raises_rpc_error(-5, 'Transaction not eligible for abandonment', lambda: alice.abandontransaction(txid=txA))
+
         self.generate(self.nodes[1], 1)
 
         # Can not abandon non-wallet transaction