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
false,
                                               m_node.args->GetIntArg("-checkaddrman", 0));
    m_node.banman = std::make_unique<BanMan>(m_args.GetDataDirBase() / "banlist", nullptr, DEFAULT_MISBEHAVING_BANTIME);
    m_node.connman = std::make_unique<ConnmanTestMsg>(0x1337, 0x1337, *m_node.addrman, *m_node.netgroupman); 
    m_node.peerman = PeerManager::make(*m_node.connman, *m_node.addrman,
                                       m_node.banman.get(), *m_node.chainman,
                                       *m_node.mempool, false);
    {
        CConnman::Options options;
        options.m_msgproc = m_node.peerman.get();
        m_node.connman->Init(options);
    }
}
TestChain100Setup::TestChain100Setup(const std::vector<const char*>& extra_args)
    : TestingSetup{CBaseChainParams::REGTEST, extra_args}
{
    SetMockTime(1598887952);
    constexpr std::array<unsigned char, 32> vchKey = {
        {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1}};
    coinbaseKey.Set(vchKey.begin(), vchKey.end(), true);
    
    this->mineBlocks(COINBASE_MATURITY);
    {
        LOCK(::cs_main);
        assert(
            m_node.chainman->ActiveChain().Tip()->GetBlockHash().ToString() ==
            "571d80a9967ae599cec0448b0b0ba1cfb606f584d8069bd7166b86854ba7a191");
    }
}
void TestChain100Setup::mineBlocks(int num_blocks)