Clarify base gas fee tests, now parametrized

Author: carver

tests/core/vm/test_london.py

@@ -16,7 +16,7 @@
 @pytest.fixture(params=MAINNET_VMS[9:])
 def london_plus_miner(request, base_db, genesis_state):
     klass = MiningChain.configure(
-        __name__='CrossoverTestChain',
+        __name__='LondonAt1',
         vm_configuration=(
             (
                 constants.GENESIS_BLOCK_NUMBER,
@@ -33,8 +33,8 @@ def london_plus_miner(request, base_db, genesis_state):
         difficulty=1,
         gas_limit=21000 * 2,  # block limit is hit with two transactions
     )
-    # On the first London+ block, it will double the block limit so that the
-    #   block *target* is hit with 2 transactions
+    # On the first London+ block, it will double the block limit so that it
+    #   can precisely hold 4 transactions.
     return klass.from_genesis(base_db, header_fields, genesis_state)
 
 
@@ -52,7 +52,8 @@ def london_plus_miner(request, base_db, genesis_state):
 def test_base_fee_evolution(
         london_plus_miner, funded_address, funded_address_private_key, num_txns, expected_base_fee):
     chain = london_plus_miner
-    assert chain.header.gas_limit == 21000 * 4
+    FOUR_TXN_GAS_LIMIT = 21000 * 4
+    assert chain.header.gas_limit == FOUR_TXN_GAS_LIMIT
 
     vm = chain.get_vm()
     txns = [
@@ -66,15 +67,15 @@ def test_base_fee_evolution(
         )
         for nonce in range(num_txns)
     ]
-    block_import, _, _ = chain.mine_all(txns, gas_limit=21000 * 4)
+    block_import, _, _ = chain.mine_all(txns, gas_limit=FOUR_TXN_GAS_LIMIT)
     mined_header = block_import.imported_block.header
-    assert mined_header.gas_limit == 21000 * 4
+    assert mined_header.gas_limit == FOUR_TXN_GAS_LIMIT
     assert mined_header.gas_used == 21000 * num_txns
     assert mined_header.base_fee_per_gas == 10 ** 9  # Initialize at 1 gwei
 
-    # Next block should have an unchanged gas fee because usage was equal to target (half of limit)
-    block_import, _, _ = chain.mine_all([], gas_limit=21000 * 4)
+    block_import, _, _ = chain.mine_all([], gas_limit=FOUR_TXN_GAS_LIMIT)
     mined_header = block_import.imported_block.header
-    assert mined_header.gas_limit == 21000 * 4
+    assert mined_header.gas_limit == FOUR_TXN_GAS_LIMIT
     assert mined_header.gas_used == 0
+    # Check that the base fee evolved correctly, depending on how much gas was used in the parent
     assert mined_header.base_fee_per_gas == expected_base_fee