For `MempoolCheck`, it seems that the intention was to have a mempool with `check_ratio = 1` (see `-checkmempool=1`):

https://github.com/bitcoin/bitcoin/blob/e66630cc87c017f40ec29f6c1edf2ed5a286e49d/src/bench/mempool_stress.cpp#L102-L116

However in the subsequent line in the above snippet, a `CTxMemPool` gets constructed with no arguments, which means that `check_ratio` will default to 0:

https://github.com/bitcoin/bitcoin/blob/e66630cc87c017f40ec29f6c1edf2ed5a286e49d/src/txmempool.h#L571

Manually specifying `check_ratio` to 1 (according to the original intention) and running the `MempoolCheck` benchmark results in an assertion error:

```
diff --git a/src/bench/mempool_stress.cpp b/src/bench/mempool_stress.cpp
index afa4618e1b..32cdb70539 100644
--- a/src/bench/mempool_stress.cpp
+++ b/src/bench/mempool_stress.cpp
@@ -105,7 +105,7 @@ static void MempoolCheck(benchmark::Bench& bench)
     const int childTxs = bench.complexityN() > 1 ? static_cast<int>(bench.complexityN()) : 2000;
     const std::vector<CTransactionRef> ordered_coins = CreateOrderedCoins(det_rand, childTxs, /* min_ancestors */ 5);
     const auto testing_setup = MakeNoLogFileContext<const TestingSetup>(CBaseChainParams::MAIN, {"-checkmempool=1"});
-    CTxMemPool pool;
+    CTxMemPool pool{nullptr, 1};
     LOCK2(cs_main, pool.cs);
     const CCoinsViewCache& coins_tip = testing_setup.get()->m_node.chainman->ActiveChainstate().CoinsTip();
     for (auto& tx : ordered_coins) AddTx(tx, pool);
```

```sh
$ ./src/bench/bench_bitcoin -filter='MempoolCheck'
...
bench_bitcoin: txmempool.cpp:759: void CTxMemPool::check(const CCoinsViewCache &, int64_t) const: Assertion `mempoolDuplicate.HaveCoin(txin.prevout)' failed.
```

Aside from this problem, we should also probably just re-use the `CTxMemPool` in `TestingSetup`.

Ping @glozow
invalid_with_cltv_tx.vin[0].scriptSig = CScript() << vchSig << 100;
        TxValidationState state;
        PrecomputedTransactionData txdata;
        BOOST_CHECK(CheckInputScripts(CTransaction(invalid_with_cltv_tx), state, m_node.chainman->ActiveChainstate().CoinsTip(), SCRIPT_VERIFY_CHECKLOCKTIMEVERIFY, true, true, txdata, nullptr));
    }
    
    {
        CMutableTransaction invalid_with_csv_tx;
        invalid_with_csv_tx.nVersion = 2;
        invalid_with_csv_tx.vin.resize(1);
        invalid_with_csv_tx.vin[0].prevout.hash = spend_tx.GetHash();
        invalid_with_csv_tx.vin[0].prevout.n = 3;
        invalid_with_csv_tx.vin[0].nSequence = 100;
        invalid_with_csv_tx.vout.resize(1);
        invalid_with_csv_tx.vout[0].nValue = 11*CENT;
        invalid_with_csv_tx.vout[0].scriptPubKey = p2pk_scriptPubKey;
        
        std::vector<unsigned char> vchSig;
        uint256 hash = SignatureHash(spend_tx.vout[3].scriptPubKey, invalid_with_csv_tx, 0, SIGHASH_ALL, 0, SigVersion::BASE);
        BOOST_CHECK(coinbaseKey.Sign(hash, vchSig));
        vchSig.push_back((unsigned char)SIGHASH_ALL);
        invalid_with_csv_tx.vin[0].scriptSig = CScript() << vchSig << 101;
        ValidateCheckInputsForAllFlags(CTransaction(invalid_with_csv_tx), SCRIPT_VERIFY_CHECKSEQUENCEVERIFY, true, m_node.chainman->ActiveChainstate().CoinsTip());
        
        invalid_with_csv_tx.vin[0].scriptSig = CScript() << vchSig << 100;
        TxValidationState state;
        PrecomputedTransactionData txdata;
        BOOST_CHECK(CheckInputScripts(CTransaction(invalid_with_csv_tx), state, &m_node.chainman->ActiveChainstate().CoinsTip(), SCRIPT_VERIFY_CHECKSEQUENCEVERIFY, true, true, txdata, nullptr));
    }