test: fix bumpfee 'spend_one_input' occasional failure

Most of the subtests in wallet_bumpfee.py expect to
find spendable UTXOs of 0.001 btc in the rbf wallet
(they use the 'spend_one_input()' method that tries
to spend one of them and if it doesn't find any, it
throws an exception).

The sporadic failure comes from the recently added
'test_feerate_checks_replaced_outputs' subtest that
can spend all them. Leaving the next subtests with
no 0.001 UTXOs to spend.

To solve it, this PR moves the recently added case
into a "context independent subtests" section.
Which is placed at the end to not affect other cases.

Author: furszy

test/functional/wallet_bumpfee.py

@@ -101,11 +101,13 @@ def run_test(self):
         test_change_script_match(self, rbf_node, dest_address)
         test_settxfee(self, rbf_node, dest_address)
         test_maxtxfee_fails(self, rbf_node, dest_address)
-        test_feerate_checks_replaced_outputs(self, rbf_node)
         # These tests wipe out a number of utxos that are expected in other tests
         test_small_output_with_feerate_succeeds(self, rbf_node, dest_address)
         test_no_more_inputs_fails(self, rbf_node, dest_address)
 
+        # Context independent tests
+        test_feerate_checks_replaced_outputs(self, rbf_node, peer_node)
+
     def test_invalid_parameters(self, rbf_node, peer_node, dest_address):
         self.log.info('Test invalid parameters')
         rbfid = spend_one_input(rbf_node, dest_address)
@@ -670,7 +672,11 @@ def test_no_more_inputs_fails(self, rbf_node, dest_address):
     self.clear_mempool()
 
 
-def test_feerate_checks_replaced_outputs(self, rbf_node):
+def test_feerate_checks_replaced_outputs(self, rbf_node, peer_node):
+    # Make sure there is enough balance
+    peer_node.sendtoaddress(rbf_node.getnewaddress(), 60)
+    self.generate(peer_node, 1)
+
     self.log.info("Test that feerate checks use replaced outputs")
     outputs = []
     for i in range(50):
@@ -693,6 +699,7 @@ def test_feerate_checks_replaced_outputs(self, rbf_node):
 
     # Bumpfee and replace all outputs with a single one using the minimum feerate
     rbf_node.bumpfee(tx_res["txid"], {"fee_rate": min_fee_rate, "outputs": new_outputs})
+    self.clear_mempool()
 
 
 if __name__ == "__main__":