test(contracts): Assert upper bound on CTC gas costs.

Previously our gas specs have only printed the values they record,
without ensuring that the cost doesn't drift up over time. Adding expectApprox will allow these costs to decrease, but not increase.

integration-tests/test/shared/utils.ts

@@ -182,11 +182,11 @@ export const expectApprox = (
 
   expect(
     actual.lte(upper),
-    `Actual value is more than ${upperPercentDeviation}% greater than target`
+    `Actual value (${actual}) is more than ${upperPercentDeviation}% greater than target (${target})`
   ).to.be.true
   expect(
     actual.gte(lower),
-    `Actual value is more than ${lowerPercentDeviation}% less than target`
+    `Actual value (${actual}) is more than ${lowerPercentDeviation}% less than target (${target})`
   ).to.be.true
 }
 

packages/contracts/test/contracts/L1/rollup/CanonicalTransactionChain.gas.spec.ts

@@ -21,6 +21,7 @@ import {
   getEthTime,
   getNextBlockNumber,
   NON_ZERO_ADDRESS,
+  expectApprox,
 } from '../../../helpers'
 
 // Still have some duplication from CanonicalTransactionChain.spec.ts, but it's so minimal that
@@ -152,14 +153,17 @@ describe('[GAS BENCHMARK] CanonicalTransactionChain', () => {
       })
 
       const receipt = await res.wait()
+      const gasUsed = receipt.gasUsed.toNumber()
 
       console.log('Benchmark complete.')
-      console.log('Gas used:', receipt.gasUsed.toNumber())
+      console.log('Gas used:', gasUsed)
+
       console.log('Fixed calldata cost:', fixedCalldataCost)
       console.log(
         'Non-calldata overhead gas cost per transaction:',
-        (receipt.gasUsed.toNumber() - fixedCalldataCost) / numTxs
+        (gasUsed - fixedCalldataCost) / numTxs
       )
+      expectApprox(gasUsed, 1_605_796, { upperPercentDeviation: 0 })
     }).timeout(10_000_000)
 
     it('200 transactions in 200 contexts', async () => {
@@ -192,14 +196,17 @@ describe('[GAS BENCHMARK] CanonicalTransactionChain', () => {
       })
 
       const receipt = await res.wait()
+      const gasUsed = receipt.gasUsed.toNumber()
 
       console.log('Benchmark complete.')
-      console.log('Gas used:', receipt.gasUsed.toNumber())
+      console.log('Gas used:', gasUsed)
+
       console.log('Fixed calldata cost:', fixedCalldataCost)
       console.log(
         'Non-calldata overhead gas cost per transaction:',
-        (receipt.gasUsed.toNumber() - fixedCalldataCost) / numTxs
+        (gasUsed - fixedCalldataCost) / numTxs
       )
+      expectApprox(gasUsed, 1_739_811, { upperPercentDeviation: 0 })
     }).timeout(10_000_000)
 
     it('100 Sequencer transactions and 100 Queue transactions in 100 contexts', async () => {
@@ -242,14 +249,17 @@ describe('[GAS BENCHMARK] CanonicalTransactionChain', () => {
       })
 
       const receipt = await res.wait()
+      const gasUsed = receipt.gasUsed.toNumber()
 
       console.log('Benchmark complete.')
-      console.log('Gas used:', receipt.gasUsed.toNumber())
+      console.log('Gas used:', gasUsed)
+
       console.log('Fixed calldata cost:', fixedCalldataCost)
       console.log(
         'Non-calldata overhead gas cost per transaction:',
-        (receipt.gasUsed.toNumber() - fixedCalldataCost) / numTxs
+        (gasUsed - fixedCalldataCost) / numTxs
       )
+      expectApprox(gasUsed, 1_126_553, { upperPercentDeviation: 0 })
     }).timeout(10_000_000)
   })
 
@@ -272,9 +282,12 @@ describe('[GAS BENCHMARK] CanonicalTransactionChain', () => {
         data
       )
       const receipt = await res.wait()
+      const gasUsed = receipt.gasUsed.toNumber()
 
       console.log('Benchmark complete.')
-      console.log('Gas used:', receipt.gasUsed.toNumber())
+      console.log('Gas used:', gasUsed)
+
+      expectApprox(gasUsed, 217_615, { upperPercentDeviation: 0 })
     })
 
     it('cost to enqueue a transaction below the prepaid threshold', async () => {
@@ -286,9 +299,12 @@ describe('[GAS BENCHMARK] CanonicalTransactionChain', () => {
         data
       )
       const receipt = await res.wait()
+      const gasUsed = receipt.gasUsed.toNumber()
 
       console.log('Benchmark complete.')
-      console.log('Gas used:', receipt.gasUsed.toNumber())
+      console.log('Gas used:', gasUsed)
+
+      expectApprox(gasUsed, 156_711, { upperPercentDeviation: 0 })
     })
   })
 })

packages/contracts/test/helpers/gas/gas.ts

+import { expect } from 'chai'
 import { ethers } from 'hardhat'
-import { Contract, Signer } from 'ethers'
+import { BigNumber, Contract, Signer } from 'ethers'
 
 export class GasMeasurement {
   GasMeasurementContract: Contract
@@ -24,3 +25,39 @@ export class GasMeasurement {
     return gasCost
   }
 }
+
+interface percentDeviationRange {
+  upperPercentDeviation: number
+  lowerPercentDeviation?: number
+}
+
+export const expectApprox = (
+  actual: BigNumber | number,
+  target: BigNumber | number,
+  { upperPercentDeviation, lowerPercentDeviation = 100 }: percentDeviationRange
+): void => {
+  actual = BigNumber.from(actual)
+  target = BigNumber.from(target)
+
+  const validDeviations =
+    upperPercentDeviation >= 0 &&
+    upperPercentDeviation <= 100 &&
+    lowerPercentDeviation >= 0 &&
+    lowerPercentDeviation <= 100
+  if (!validDeviations) {
+    throw new Error(
+      'Upper and lower deviation percentage arguments should be between 0 and 100'
+    )
+  }
+  const upper = target.mul(100 + upperPercentDeviation).div(100)
+  const lower = target.mul(100 - lowerPercentDeviation).div(100)
+
+  expect(
+    actual.lte(upper),
+    `Actual value (${actual}) is more than ${upperPercentDeviation}% greater than target (${target})`
+  ).to.be.true
+  expect(
+    actual.gte(lower),
+    `Actual value (${actual}) is more than ${lowerPercentDeviation}% less than target (${target})`
+  ).to.be.true
+}