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.

}
/**
 * Check whether all of this transaction's input scripts succeed.
 *
 * This involves ECDSA signature checks so can be computationally intensive. This function should
 * only be called after the cheap sanity checks in CheckTxInputs passed.
 *
 * If pvChecks is not nullptr, script checks are pushed onto it instead of being performed inline. Any
 * script checks which are not necessary (eg due to script execution cache hits) are, obviously,
 * not pushed onto pvChecks/run.
 *
 * Setting cacheSigStore/cacheFullScriptStore to false will remove elements from the corresponding cache
 * which are matched. This is useful for checking blocks where we will likely never need the cache
 * entry again.
 *
 * Note that we may set state.reason to NOT_STANDARD for extra soft-fork flags in flags, block-checking
 * callers should probably reset it to CONSENSUS in such cases.
 *
 * Non-static (and re-declared) in src/test/txvalidationcache_tests.cpp
 */
bool CheckInputScripts(const CTransaction& tx, TxValidationState &state, const CCoinsViewCache &inputs, unsigned int flags, bool cacheSigStore, bool cacheFullScriptStore, PrecomputedTransactionData& txdata, std::vector<CScriptCheck> *pvChecks) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
{
    if (tx.IsCoinBase()) return true;
    if (pvChecks) {
        pvChecks->reserve(tx.vin.size());
    }