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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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.

bool FlushStateToDisk(
        const CChainParams& chainparams,
        BlockValidationState &state,
        FlushStateMode mode,
        int nManualPruneHeight = 0);
    
    void ForceFlushStateToDisk();
    
    
    void PruneAndFlush();
    /**
     * Make the best chain active, in multiple steps. The result is either failure
     * or an activated best chain. pblock is either nullptr or a pointer to a block
     * that is already loaded (to avoid loading it again from disk).
     *
     * ActivateBestChain is split into steps (see ActivateBestChainStep) so that
     * we avoid holding cs_main for an extended period of time; the length of this
     * call may be quite long during reindexing or a substantial reorg.
     *
     * May not be called with cs_main held. May not be called in a
     * validationinterface callback.
     *
     * @returns true unless a system error occurred
     */
    bool ActivateBestChain(
        BlockValidationState& state,
        const CChainParams& chainparams,
        std::shared_ptr<const CBlock> pblock) LOCKS_EXCLUDED(cs_main);
    bool AcceptBlock(const std::shared_ptr<const CBlock>& pblock, BlockValidationState& state, const CChainParams& chainparams, CBlockIndex** ppindex, bool fRequested, const FlatFilePos* dbp, bool* fNewBlock) EXCLUSIVE_LOCKS_REQUIRED(cs_main);