Merge pull request #4658 from ethereum-optimism/jm/ctb-test-large-gaps

test(ctb): Add a fuzz test for large deposit gaps

.changeset/tough-avocados-dance.md

+---
+'@eth-optimism/contracts-bedrock': patch
+---
+
+Added a test for large deposit gaps

packages/contracts-bedrock/.gas-snapshot

@@ -368,14 +368,14 @@ RLPWriter_Test:test_writeUint_smallint3_succeeds() (gas: 7311)
 RLPWriter_Test:test_writeUint_smallint4_succeeds() (gas: 7312)
 RLPWriter_Test:test_writeUint_smallint_succeeds() (gas: 7290)
 RLPWriter_Test:test_writeUint_zero_succeeds() (gas: 7802)
-ResourceMetering_Test:test_meter_initialResourceParams_succeeds() (gas: 8965)
-ResourceMetering_Test:test_meter_updateNoGasDelta_succeeds() (gas: 2008101)
-ResourceMetering_Test:test_meter_updateOneEmptyBlock_succeeds() (gas: 18152)
-ResourceMetering_Test:test_meter_updateParamsNoChange_succeeds() (gas: 13911)
-ResourceMetering_Test:test_meter_updateTenEmptyBlocks_succeeds() (gas: 20900)
-ResourceMetering_Test:test_meter_updateTwoEmptyBlocks_succeeds() (gas: 20923)
-ResourceMetering_Test:test_meter_useMax_succeeds() (gas: 8017204)
-ResourceMetering_Test:test_meter_useMoreThanMax_reverts() (gas: 16023)
+ResourceMetering_Test:test_meter_initialResourceParams_succeeds() (gas: 8983)
+ResourceMetering_Test:test_meter_updateNoGasDelta_succeeds() (gas: 2008119)
+ResourceMetering_Test:test_meter_updateOneEmptyBlock_succeeds() (gas: 18148)
+ResourceMetering_Test:test_meter_updateParamsNoChange_succeeds() (gas: 13859)
+ResourceMetering_Test:test_meter_updateTenEmptyBlocks_succeeds() (gas: 20918)
+ResourceMetering_Test:test_meter_updateTwoEmptyBlocks_succeeds() (gas: 20941)
+ResourceMetering_Test:test_meter_useMax_succeeds() (gas: 8017151)
+ResourceMetering_Test:test_meter_useMoreThanMax_reverts() (gas: 16045)
 Semver_Test:test_behindProxy_succeeds() (gas: 506725)
 Semver_Test:test_version_succeeds() (gas: 9396)
 SequencerFeeVault_Test:test_constructor_succeeds() (gas: 5504)

packages/contracts-bedrock/contracts/test/ResourceMetering.t.sol

@@ -108,4 +108,18 @@ contract ResourceMetering_Test is CommonTest {
         vm.expectRevert("ResourceMetering: cannot buy more gas than available gas limit");
         meter.use(target * elasticity + 1);
     }
+
+    // Demonstrates that the resource metering arithmetic can tolerate very large gaps between
+    // deposits.
+    function testFuzz_meter_largeBlockDiff_succeeds(uint64 _amount, uint256 _blockDiff) external {
+        // This test fails if the following line is commented out.
+        // At 12 seconds per block, this number is effectively unreachable.
+        vm.assume(_blockDiff < 433576281058164217753225238677900874458691);
+
+        uint64 target = uint64(uint256(meter.TARGET_RESOURCE_LIMIT()));
+        uint64 elasticity = uint64(uint256(meter.ELASTICITY_MULTIPLIER()));
+        vm.assume(_amount < target * elasticity);
+        vm.roll(initialBlockNum + _blockDiff);
+        meter.use(_amount);
+    }
 }