fix: address flake in fee settings test (#21991)

`fee_settings.test.ts` could flake because its two `proveTx` calls could
read different `getCurrentMinFees()` values if the node synced L1 state
in between. This change makes the behavior test deterministic by waiting
until the deploy block is checkpointed, taking a baseline fee snapshot,
and preparing both transactions against controlled fee snapshots. It
also adds a deterministic regression test that forces different fee
snapshots for the two `proveTx` calls and reproduces the original
stale-snapshot race directly.`

Author: LHerskind

yarn-project/end-to-end/src/e2e_fees/fee_settings.test.ts

@@ -1,12 +1,14 @@
 import type { AztecAddress } from '@aztec/aztec.js/addresses';
 import type { AztecNode } from '@aztec/aztec.js/node';
 import { CheatCodes } from '@aztec/aztec/testing';
+import type { BlockNumber } from '@aztec/foundation/branded-types';
 import { Fr } from '@aztec/foundation/curves/bn254';
 import { retryUntil } from '@aztec/foundation/retry';
 import { TestContract } from '@aztec/noir-test-contracts.js/Test';
-import type { GasSettings } from '@aztec/stdlib/gas';
+import type { GasFees, GasSettings } from '@aztec/stdlib/gas';
 import { TX_ERROR_INSUFFICIENT_FEE_PER_GAS } from '@aztec/stdlib/tx';
 
+import { jest } from '@jest/globals';
 import { inspect } from 'util';
 
 import type { TestWallet } from '../test-wallet/test_wallet.js';
@@ -20,13 +22,18 @@ describe('e2e_fees fee settings', () => {
   let wallet: TestWallet;
   let gasSettings: Partial<GasSettings>;
   let testContract: TestContract;
+  let testContractDeployBlock: BlockNumber;
   const t = new FeesTest('fee_juice', 1);
 
   beforeAll(async () => {
     await t.setup();
     ({ aliceAddress, wallet, gasSettings, cheatCodes, aztecNode } = t);
 
-    ({ contract: testContract } = await TestContract.deploy(wallet).send({ from: aliceAddress }));
+    const deployedTestContract = await TestContract.deploy(wallet).send({
+      from: aliceAddress,
+    });
+    testContract = deployedTestContract.contract;
+    testContractDeployBlock = deployedTestContract.receipt.blockNumber!;
     gasSettings = { ...gasSettings, maxFeesPerGas: undefined };
   });
 
@@ -39,21 +46,39 @@ describe('e2e_fees fee settings', () => {
       const before = await aztecNode.getCurrentMinFees();
       t.logger.info(`Initial L2 min fees are ${inspect(before)}`, { minFees: before.toInspect() });
       await cheatCodes.rollup.bumpProvingCostPerMana(current => (current * 120n) / 100n);
-      await retryUntil(
+      return await retryUntil(
         async () => {
           const after = await aztecNode.getCurrentMinFees();
           t.logger.info(`L2 min fees are now ${inspect(after)}`, {
             minFeesBefore: before.toInspect(),
             minFeesAfter: after.toInspect(),
           });
-          return after.feePerL2Gas > before.feePerL2Gas;
+          return after.feePerL2Gas > before.feePerL2Gas ? after : undefined;
         },
         'L2 min fee increase',
         5,
         1,
       );
     };
 
+    // Pick a baseline from the post-checkpoint chain state. The prove step itself is
+    // made deterministic by prepareTxsWithMockedMinFees below.
+    const getCurrentMinFeesAfterCheckpoint = async (checkpointedBlock: BlockNumber) => {
+      return await retryUntil(
+        async () => {
+          const currentCheckpointedBlock = await aztecNode.getCheckpointedBlockNumber();
+          if (currentCheckpointedBlock < checkpointedBlock) {
+            return undefined;
+          }
+
+          return await aztecNode.getCurrentMinFees();
+        },
+        `L2 min fees after block ${checkpointedBlock} is checkpointed`,
+        60,
+        1,
+      );
+    };
+
     const proveTx = async (minFeePadding: number | undefined) => {
       t.logger.info(`Preparing tx to be sent with min fee padding ${minFeePadding}`);
       wallet.setMinFeePadding(minFeePadding);
@@ -66,18 +91,61 @@ describe('e2e_fees fee settings', () => {
       return tx;
     };
 
+    const prepareTxsWithMockedMinFees = async (noPaddingMinFees: GasFees, defaultPaddingMinFees: GasFees) => {
+      const getCurrentMinFeesSpy = jest
+        .spyOn(aztecNode, 'getCurrentMinFees')
+        .mockResolvedValueOnce(noPaddingMinFees)
+        .mockResolvedValueOnce(defaultPaddingMinFees);
+
+      try {
+        const txWithNoPadding = await proveTx(0);
+        const txWithDefaultPadding = await proveTx(undefined);
+        return { txWithNoPadding, txWithDefaultPadding };
+      } finally {
+        getCurrentMinFeesSpy.mockRestore();
+      }
+    };
+
     it('handles min fee spikes with default padding', async () => {
-      // Prepare two txs using the current L2 min fees: one with no padding and one with default padding
-      const txWithNoPadding = await proveTx(0);
-      const txWithDefaultPadding = await proveTx(undefined);
+      const stableMinFees = await getCurrentMinFeesAfterCheckpoint(testContractDeployBlock);
+      const { txWithNoPadding, txWithDefaultPadding } = await prepareTxsWithMockedMinFees(stableMinFees, stableMinFees);
+
+      expect(txWithNoPadding.data.constants.txContext.gasSettings.maxFeesPerGas.equals(stableMinFees)).toBe(true);
+      expect(
+        txWithDefaultPadding.data.constants.txContext.gasSettings.maxFeesPerGas.equals(stableMinFees.mul(1.5)),
+      ).toBe(true);
 
       // Now bump the L2 fees before we actually send them
-      await bumpL2Fees();
+      const bumpedMinFees = await bumpL2Fees();
+      expect(stableMinFees.feePerL2Gas).toBeLessThan(bumpedMinFees.feePerL2Gas);
+      expect(stableMinFees.mul(1.5).feePerL2Gas).toBeGreaterThan(bumpedMinFees.feePerL2Gas);
 
       // And check that the no-padding does not get mined, but the default padding is good enough
-      t.logger.info(`Sendings txs`);
+      t.logger.info(`Sending txs`);
       await expect(txWithNoPadding.send()).rejects.toThrow(TX_ERROR_INSUFFICIENT_FEE_PER_GAS);
       await expect(txWithDefaultPadding.send()).resolves.toBeDefined();
     });
+
+    it('reproduces the stale fee snapshot race deterministically', async () => {
+      const lowerMinFees = await getCurrentMinFeesAfterCheckpoint(testContractDeployBlock);
+      const higherMinFees = lowerMinFees.mul(2);
+
+      const { txWithNoPadding, txWithDefaultPadding } = await prepareTxsWithMockedMinFees(higherMinFees, lowerMinFees);
+
+      expect(txWithNoPadding.data.constants.txContext.gasSettings.maxFeesPerGas.equals(higherMinFees)).toBe(true);
+      expect(
+        txWithDefaultPadding.data.constants.txContext.gasSettings.maxFeesPerGas.equals(lowerMinFees.mul(1.5)),
+      ).toBe(true);
+
+      const bumpedMinFees = await bumpL2Fees();
+      expect(lowerMinFees.feePerL2Gas).toBeLessThan(bumpedMinFees.feePerL2Gas);
+      expect(higherMinFees.feePerL2Gas).toBeGreaterThan(bumpedMinFees.feePerL2Gas);
+      expect(lowerMinFees.mul(1.5).feePerL2Gas).toBeGreaterThan(bumpedMinFees.feePerL2Gas);
+
+      // This is the original flake: the "no padding" tx only succeeds because it was
+      // accidentally prepared against an earlier, higher fee snapshot than the padded tx.
+      await expect(txWithNoPadding.send()).resolves.toBeDefined();
+      await expect(txWithDefaultPadding.send()).resolves.toBeDefined();
+    });
   });
 });