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
static inline uint64_t InsecureRandRange(uint64_t range) { return g_insecure_rand_ctx.randrange(range); }
static inline bool InsecureRandBool() { return g_insecure_rand_ctx.randbool(); }
static constexpr CAmount CENT{1000000};
/** Basic testing setup.
 * This just configures logging, data dir and chain parameters.
 */
struct BasicTestingSetup {
    ECCVerifyHandle globalVerifyHandle;
    node::NodeContext m_node;
    explicit BasicTestingSetup(const std::string& chainName = CBaseChainParams::MAIN, const std::vector<const char*>& extra_args = {});
    ~BasicTestingSetup();
    const fs::path m_path_root;
    ArgsManager m_args;
};
/** Testing setup that performs all steps up until right before
 * ChainstateManager gets initialized. Meant for testing ChainstateManager
 * initialization behaviour.
 */
struct ChainTestingSetup : public BasicTestingSetup {
    node::CacheSizes m_cache_sizes{};
    explicit ChainTestingSetup(const std::string& chainName = CBaseChainParams::MAIN, const std::vector<const char*>& extra_args = {});
    ~ChainTestingSetup();
};
/** Testing setup that configures a complete environment.
 */
struct TestingSetup : public ChainTestingSetup {
    explicit TestingSetup(const std::string& chainName = CBaseChainParams::MAIN, const std::vector<const char*>& extra_args = {});
};
struct RegTestingSetup : public TestingSetup {
    RegTestingSetup()