Add test coverage for bump fee calculation failure in feebumper #34902

1. 
   rkrux commented at 1:33 pm on March 23, 2026: contributor

   Motivation

   There is no test coverage for the error here: https://github.com/bitcoin/bitcoin/blob/1a1f584360ce053f9f832e310d063d686f86c6d7/src/wallet/feebumper.cpp#L84-L86

   Lack of coverage can be seen for line 85 (currently) here: https://maflcko.github.io/b-c-cov/total.coverage/src/wallet/feebumper.cpp.gcov.html

   Possible solution

   A functional test using the bumpfee RPC can be a possible solution. There is a wallet_bumpfee test file that has a good amunt of tests, which can be referred to come up with a solution.

   Useful Skills

   • Compiling Bitcoin Core from source
   • Running the C++ unit tests and the Python functional tests
   • Wallet transaction creation
   • Handling unconfirmed UTXOs while creating and bumping wallet transactions
   • Fee rate and mempool fee environment theoretical knowledge

   Guidance for new contributors

   Want to work on this issue?

   For guidance on contributing, please read CONTRIBUTING.md before opening your pull request.

2. rkrux added the label good first issue on Mar 23, 2026
3. 
   aya119119 commented at 2:52 pm on March 23, 2026: none

   eloo I’de take this onee
4. 
   furszy commented at 2:56 pm on March 23, 2026: member

   @aya119119 awesome, welcome to Core. Feel free to tag me when you create the PR for it.

Contributors
rkrux aya119119 furszy

Labels
good first issue