Merge bitcoin/bitcoin#29735: AcceptMultipleTransactions: Fix workspace not being set as client_maxfeerate failure

4ba1d0b553 fuzz: Add coverage for client_maxfeerate (Greg Sanders)
91d7d8f22a AcceptMultipleTransactions: Fix workspace client_maxfeerate (Greg Sanders)
f3aa5bd5eb fill_mempool: assertions and docsctring update (Greg Sanders)
a3da63e8fe Move fill_mempool to util function (Greg Sanders)
73b68bd8b4 fill_mempool: remove subtest-specific comment (Greg Sanders)

Pull request description:

  Bug causes an `Assume()` failure due to the expectation that the individual result should be invalid when done over `submitpackage` via rpc.

  Bug introduced by https://github.com/bitcoin/bitcoin/pull/28950 , and I discovered it rebasing https://github.com/bitcoin/bitcoin/pull/28984 since it's easier to hit in that test scenario.

  Tests in place were only checking `AcceptSingleTransaction`-level checks due to package evaluation only triggering when minfee is too high for the parent transaction.

  Added test along with fix, moving the fill_mempool utility into a common area for re-use.

ACKs for top commit:
  glozow:
    reACK 4ba1d0b553
  theStack:
    ACK 4ba1d0b553
  ismaelsadeeq:
    re-ACK 4ba1d0b553  via [diff](4fe7d150eb..4ba1d0b553)

Tree-SHA512: 3729bdf7f25d04e232f173ccee04ddbb2afdaafa3d04292a01cecf58fb11b3b2bc133e8490277f1a67622b62d17929c242dc980f9bb647896beea4332ee35306

test/functional/test_framework/util.py

@@ -496,6 +496,55 @@ def check_node_connections(*, node, num_in, num_out):
     assert_equal(info["connections_in"], num_in)
     assert_equal(info["connections_out"], num_out)
 
+def fill_mempool(test_framework, node, miniwallet):
+    """Fill mempool until eviction.
+
+    Allows for simpler testing of scenarios with floating mempoolminfee > minrelay
+    Requires -datacarriersize=100000 and
+   -maxmempool=5.
+    It will not ensure mempools become synced as it
+    is based on a single node and assumes -minrelaytxfee
+    is 1 sat/vbyte.
+    """
+    test_framework.log.info("Fill the mempool until eviction is triggered and the mempoolminfee rises")
+    txouts = gen_return_txouts()
+    relayfee = node.getnetworkinfo()['relayfee']
+
+    assert_equal(relayfee, Decimal('0.00001000'))
+
+    tx_batch_size = 1
+    num_of_batches = 75
+    # Generate UTXOs to flood the mempool
+    # 1 to create a tx initially that will be evicted from the mempool later
+    # 75 transactions each with a fee rate higher than the previous one
+    test_framework.generate(miniwallet, 1 + (num_of_batches * tx_batch_size))
+
+    # Mine COINBASE_MATURITY - 1 blocks so that the UTXOs are allowed to be spent
+    test_framework.generate(node, 100 - 1)
+
+    test_framework.log.debug("Create a mempool tx that will be evicted")
+    tx_to_be_evicted_id = miniwallet.send_self_transfer(from_node=node, fee_rate=relayfee)["txid"]
+
+    # Increase the tx fee rate to give the subsequent transactions a higher priority in the mempool
+    # The tx has an approx. vsize of 65k, i.e. multiplying the previous fee rate (in sats/kvB)
+    # by 130 should result in a fee that corresponds to 2x of that fee rate
+    base_fee = relayfee * 130
+
+    test_framework.log.debug("Fill up the mempool with txs with higher fee rate")
+    with node.assert_debug_log(["rolling minimum fee bumped"]):
+        for batch_of_txid in range(num_of_batches):
+            fee = (batch_of_txid + 1) * base_fee
+            create_lots_of_big_transactions(miniwallet, node, fee, tx_batch_size, txouts)
+
+    test_framework.log.debug("The tx should be evicted by now")
+    # The number of transactions created should be greater than the ones present in the mempool
+    assert_greater_than(tx_batch_size * num_of_batches, len(node.getrawmempool()))
+    # Initial tx created should not be present in the mempool anymore as it had a lower fee rate
+    assert tx_to_be_evicted_id not in node.getrawmempool()
+
+    test_framework.log.debug("Check that mempoolminfee is larger than minrelaytxfee")
+    assert_equal(node.getmempoolinfo()['minrelaytxfee'], Decimal('0.00001000'))
+    assert_greater_than(node.getmempoolinfo()['mempoolminfee'], Decimal('0.00001000'))
 
 # Transaction/Block functions
 #############################