test: check that bumpfee RPC fails for txs with descendants in mempool

This commit adds missing test coverage for the bumpfee RPC
error "Transaction has descendants in the mempool", which is
thrown if the bumped tx has descendants in the mempool and is
_not_ connected to the bitcoin wallet. To achieve that, the
test framework's MiniWallet is used.

Author: theStack

test/functional/wallet_bumpfee.py

@@ -32,6 +32,8 @@
     assert_greater_than,
     assert_raises_rpc_error,
 )
+from test_framework.wallet import MiniWallet
+
 
 WALLET_PASSPHRASE = "test"
 WALLET_PASSPHRASE_TIMEOUT = 3600
@@ -265,6 +267,14 @@ def test_bumpfee_with_descendant_fails(self, rbf_node, rbf_node_address, dest_ad
     tx = rbf_node.signrawtransactionwithwallet(tx)
     rbf_node.sendrawtransaction(tx["hex"])
     assert_raises_rpc_error(-8, "Transaction has descendants in the wallet", rbf_node.bumpfee, parent_id)
+
+    # create tx with descendant in the mempool by using MiniWallet
+    miniwallet = MiniWallet(rbf_node)
+    parent_id = spend_one_input(rbf_node, miniwallet.get_address())
+    tx = rbf_node.gettransaction(txid=parent_id, verbose=True)['decoded']
+    miniwallet.scan_tx(tx)
+    miniwallet.send_self_transfer(from_node=rbf_node)
+    assert_raises_rpc_error(-8, "Transaction has descendants in the mempool", rbf_node.bumpfee, parent_id)
     self.clear_mempool()