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.

static const int64_t DEFAULT_MAX_TIP_AGE = 24 * 60 * 60;
static const bool DEFAULT_CHECKPOINTS_ENABLED = true;
static const bool DEFAULT_TXINDEX = false;
static const char* const DEFAULT_BLOCKFILTERINDEX = "0";
static const bool DEFAULT_PERSIST_MEMPOOL = true;
static const bool DEFAULT_FEEFILTER = true;
static const int DEFAULT_STOPATHEIGHT = 0;
static const unsigned int MIN_BLOCKS_TO_KEEP = 288;
static const signed int DEFAULT_CHECKBLOCKS = 6;
static const unsigned int DEFAULT_CHECKLEVEL = 3;
static const uint64_t MIN_DISK_SPACE_FOR_BLOCK_FILES = 550 * 1024 * 1024;
static constexpr size_t MINIMUM_WITNESS_COMMITMENT{38};
struct BlockHasher
{
    
    
    
    size_t operator()(const uint256& hash) const { return ReadLE64(hash.begin()); }
};
enum class SynchronizationState {
    INIT_REINDEX,
    INIT_DOWNLOAD,
    POST_INIT
};
extern RecursiveMutex cs_main;
extern CBlockPolicyEstimator feeEstimator;
typedef std::unordered_map<uint256, CBlockIndex*, BlockHasher> BlockMap;
extern Mutex g_best_block_mutex;
extern std::condition_variable g_best_block_cv;
extern uint256 g_best_block;