Merge bitcoin/bitcoin#25358: test: passing a value below 5 MB to -maxmempool should throw an error

216c9b0 test: passing a value below 5 MB to -maxmempool should throw an error (brunoerg)

Pull request description:

  This PR adds test coverage for the following init error:
  https://github.com/bitcoin/bitcoin/blob/5174a139c92c1238f9700d06e362dc628d81a0a9/src/init.cpp#L931-L935

  By default, the minimum value is 5 MB. See:
  https://github.com/bitcoin/bitcoin/blob/master/doc/reduce-memory.md#memory-pool

ACKs for top commit:
  laanwj:
    Code review ACK 216c9b0
  furszy:
    Code review ACK 216c9b0

Tree-SHA512: 0c8fdcefb85e3dabb986a6294ad18503168a04246926614cbfa2d09d9e997312c937b01994f2999b1dc583e2eac5cdb8058bd58577baeb3eb23fdc690400cab9

Author: MacroFake

test/functional/mempool_limit.py

@@ -77,6 +77,10 @@ def run_test(self):
         self.log.info('Create a mempool tx that will not pass mempoolminfee')
         assert_raises_rpc_error(-26, "mempool min fee not met", miniwallet.send_self_transfer, from_node=node, fee_rate=relayfee)
 
+        self.log.info('Test passing a value below the minimum (5 MB) to -maxmempool throws an error')
+        self.stop_node(0)
+        self.nodes[0].assert_start_raises_init_error(["-maxmempool=4"], "Error: -maxmempool must be at least 5 MB")
+
 
 if __name__ == '__main__':
     MempoolLimitTest().main()