test: cover unused mempool space in coins cache limit #35490

1. 
   w0xlt commented at 12:05 AM on June 9, 2026: contributor

   This PR adds a unit test for Chainstate::GetCoinsCacheSizeState().

   Chainstate::GetCoinsCacheSizeState() calculates when the UTXO/coins cache is too large and should be flushed. Part of that calculation includes unused -maxmempool space. For example, if the mempool limit is 300 MiB but the mempool is mostly empty, some of that unused space can be counted toward the coins cache limit.

   The existing validation_flush_tests.cpp test checks this calculation by calling:

   chainstate.GetCoinsCacheSizeState(MAX_COINS_BYTES, max_mempool_size_bytes)
   

   This new test checks the no-argument call:

   chainstate.GetCoinsCacheSizeState()
   

   That is the call used by validation code during normal operation.

   The test grows the coins cache above the coins-only limit, then checks that:

   • calling the explicit helper with max_mempool_size_bytes=0 reports CRITICAL
   • calling the normal no-argument method does not report CRITICAL, because it includes unused mempool space

   This makes sure future refactors do not accidentally drop unused mempool space from the normal cache-size calculation.

2. test: cover unused mempool space in coins cache 843f163c66
3. DrahtBot added the label Tests on Jun 9, 2026
4. 
   DrahtBot commented at 12:06 AM on June 9, 2026: contributor

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   The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

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   Code Coverage & Benchmarks

   For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/35490.

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5. 
   sedited commented at 7:42 AM on June 9, 2026: contributor

   Concept ACK

6. sedited requested review from l0rinc on Jun 9, 2026

Review Requested
l0rinc