When testing a transaction for mempool acceptance, the fee must be calculated anyway. Thus, with minimal complexity overhead, the testmempoolaccept RPC could return the fee to the user.

#### Useful skills:

Basic understanding of the mempool, the Bitcoin Core RPC interface, and the functional test framework.

#### Want to work on this issue?

The purpose of the `good first issue` label is to highlight which issues are suitable for a new contributor without a deep understanding of the codebase.

You do not need to request permission to start working on this. You are encouraged to comment on the issue if you are planning to work on it. This will help other contributors monitor which issues are actively being addressed and is also an effective way to request assistance if and when you need it.

For guidance on contributing, please read [CONTRIBUTING.md](https://github.com/bitcoin/bitcoin/blob/master/CONTRIBUTING.md) before opening your pull request.

};
void InitScriptExecutionCache();
bool ReadBlockFromDisk(CBlock& block, const FlatFilePos& pos, const Consensus::Params& consensusParams);
bool ReadBlockFromDisk(CBlock& block, const CBlockIndex* pindex, const Consensus::Params& consensusParams);
bool ReadRawBlockFromDisk(std::vector<uint8_t>& block, const FlatFilePos& pos, const CMessageHeader::MessageStartChars& message_start);
bool ReadRawBlockFromDisk(std::vector<uint8_t>& block, const CBlockIndex* pindex, const CMessageHeader::MessageStartChars& message_start);
bool UndoReadFromDisk(CBlockUndo& blockundo, const CBlockIndex* pindex);
bool CheckBlock(const CBlock& block, BlockValidationState& state, const Consensus::Params& consensusParams, bool fCheckPOW = true, bool fCheckMerkleRoot = true);
bool TestBlockValidity(BlockValidationState& state, const CChainParams& chainparams, const CBlock& block, CBlockIndex* pindexPrev, bool fCheckPOW = true, bool fCheckMerkleRoot = true) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
/** Check whether witness commitments are required for a block, and whether to enforce NULLDUMMY (BIP 147) rules.
 *  Note that transaction witness validation rules are always enforced when P2SH is enforced. */
bool IsWitnessEnabled(const CBlockIndex* pindexPrev, const Consensus::Params& params);
int GetWitnessCommitmentIndex(const CBlock& block);
void UpdateUncommittedBlockStructures(CBlock& block, const CBlockIndex* pindexPrev, const Consensus::Params& consensusParams);
std::vector<unsigned char> GenerateCoinbaseCommitment(CBlock& block, const CBlockIndex* pindexPrev, const Consensus::Params& consensusParams);
class CVerifyDB {
public:
    CVerifyDB();
    ~CVerifyDB();
    bool VerifyDB(const CChainParams& chainparams, CCoinsView *coinsview, int nCheckLevel, int nCheckDepth);
};
CBlockIndex* LookupBlockIndex(const uint256& hash) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
CBlockIndex* FindForkInGlobalIndex(const CChain& chain, const CBlockLocator& locator) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
enum DisconnectResult