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.

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

DisconnectResult DisconnectBlock(const CBlock& block, const CBlockIndex* pindex, CCoinsViewCache& view);
    bool ConnectBlock(const CBlock& block, BlockValidationState& state, CBlockIndex* pindex,
                      CCoinsViewCache& view, const CChainParams& chainparams, bool fJustCheck = false) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
    
    bool DisconnectTip(BlockValidationState& state, const CChainParams& chainparams, DisconnectedBlockTransactions* disconnectpool) EXCLUSIVE_LOCKS_REQUIRED(cs_main, m_mempool.cs);
    
    bool PreciousBlock(BlockValidationState& state, const CChainParams& params, CBlockIndex* pindex) LOCKS_EXCLUDED(cs_main);
    bool InvalidateBlock(BlockValidationState& state, const CChainParams& chainparams, CBlockIndex* pindex) LOCKS_EXCLUDED(cs_main);
    void ResetBlockFailureFlags(CBlockIndex* pindex) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
    
    bool ReplayBlocks(const CChainParams& params);
    bool RewindBlockIndex(const CChainParams& params) LOCKS_EXCLUDED(cs_main);
    bool LoadGenesisBlock(const CChainParams& chainparams);
    void PruneBlockIndexCandidates();
    void UnloadBlockIndex();
    
    bool IsInitialBlockDownload() const;
    /**
     * Make various assertions about the state of the block index.
     *
     * By default this only executes fully when using the Regtest chain; see: fCheckBlockIndex.
     */
    void CheckBlockIndex(const Consensus::Params& consensusParams);
    
    void LoadMempool(const ArgsManager& args);
    
    bool LoadChainTip(const CChainParams& chainparams) EXCLUSIVE_LOCKS_REQUIRED(cs_main);