fix: Add transaction simulation supported networks global mock (#30507)

## **Description**

A global mock has been added for the "supported networks" check made as
part of the transaction simulations feature. This is triggered by
certain types of confirmations (those that support transaction
simulations), so it's triggered by a wide variety of E2E tests.

[![Open in GitHub
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## **Related issues**

Fixes #30490

## **Manual testing steps**

This should resolve the privacy snapshot related errors on CI.

You could also double-check that the mocked response is returned by
running an e2e test locally that uses a confirmation that supports
transaction simulation, then inspecting the network tab of the service
worker dev console while the test is running, and checking the response
to the
`https://tx-sentinel-ethereum-mainnet.api.cx.metamask.io/networks` call

## **Screenshots/Recordings**

N/A

## **Pre-merge author checklist**

- [x] I've followed [MetaMask Contributor
Docs](https://github.com/MetaMask/contributor-docs) and [MetaMask
Extension Coding
Standards](https://github.com/MetaMask/metamask-extension/blob/main/.github/guidelines/CODING_GUIDELINES.md).
- [x] I've completed the PR template to the best of my ability
- [x] I’ve included tests if applicable
- [x] I’ve documented my code using [JSDoc](https://jsdoc.app/) format
if applicable
- [x] I’ve applied the right labels on the PR (see [labeling
guidelines](https://github.com/MetaMask/metamask-extension/blob/main/.github/guidelines/LABELING_GUIDELINES.md)).
Not required for external contributors.

## **Pre-merge reviewer checklist**

- [ ] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [ ] I confirm that this PR addresses all acceptance criteria described
in the ticket it closes and includes the necessary testing evidence such
as recordings and or screenshots.

---------

Co-authored-by: seaona <[email protected]>

shared/constants/transaction.ts

@@ -199,3 +199,10 @@ export enum TokenStandard {
   /** Not a token, but rather the base asset of the selected chain. */
   none = 'NONE',
 }
+
+/**
+ * The hostname used for Ethereum Mainnet transaction simulations, and for
+ * retrieving metadata for transaction simulation supported networks.
+ */
+export const TX_SENTINEL_URL =
+  'https://tx-sentinel-ethereum-mainnet.api.cx.metamask.io';

test/e2e/mock-e2e.js

@@ -16,6 +16,7 @@ const {
   SWAPS_API_V2_BASE_URL,
   TOKEN_API_BASE_URL,
 } = require('../../shared/constants/swaps');
+const { TX_SENTINEL_URL } = require('../../shared/constants/transaction');
 const { SECURITY_ALERTS_PROD_API_BASE_URL } = require('./tests/ppom/constants');
 const {
   DEFAULT_FEATURE_FLAGS_RESPONSE: BRIDGE_DEFAULT_FEATURE_FLAGS_RESPONSE,
@@ -314,6 +315,21 @@ async function setupMocking(
       };
     });
 
+  // This endpoint returns metadata for "transaction simulation" supported networks.
+  await server.forGet(`${TX_SENTINEL_URL}/networks`).thenJson(200, {
+    1: {
+      name: 'Mainnet',
+      group: 'ethereum',
+      chainID: 1,
+      nativeCurrency: { name: 'ETH', symbol: 'ETH', decimals: 18 },
+      network: 'ethereum-mainnet',
+      explorer: 'https://etherscan.io',
+      confirmations: true,
+      smartTransactions: true,
+      hidden: false,
+    },
+  });
+
   await server
     .forGet(`${SWAPS_API_V2_BASE_URL}/featureFlags`)
     .thenCallback(() => {

test/e2e/tests/simulation-details/simulation-details.spec.ts

@@ -1,6 +1,7 @@
 import { hexToNumber } from '@metamask/utils';
 import { Mockttp, MockttpServer } from 'mockttp';
 import { CHAIN_IDS } from '../../../../shared/constants/network';
+import { TX_SENTINEL_URL } from '../../../../shared/constants/transaction';
 import FixtureBuilder from '../../fixture-builder';
 import {
   createDappTransaction,
@@ -43,15 +44,6 @@ import {
 } from './mock-request-send-eth';
 import { MockRequestResponse } from './types';
 
-const TX_SENTINEL_URL =
-  'https://tx-sentinel-ethereum-mainnet.api.cx.metamask.io/';
-
-const mockNetworkRequest = async (mockServer: Mockttp) => {
-  await mockServer.forGet(`${TX_SENTINEL_URL}/networks`).thenJson(200, {
-    '1': { name: 'Mainnet', confirmations: true },
-  });
-};
-
 async function withFixturesForSimulationDetails(
   {
     title,
@@ -64,17 +56,13 @@ async function withFixturesForSimulationDetails(
   },
   test: (args: Pick<Fixtures, 'driver' | 'mockServer'>) => Promise<void>,
 ) {
-  const testSpecificMock = async (mockServer: MockttpServer) => {
-    await mockNetworkRequest(mockServer);
-    await mockRequests(mockServer);
-  };
   await withFixtures(
     {
       fixtures: new FixtureBuilder({ inputChainId })
         .withPermissionControllerConnectedToTestDapp()
         .build(),
       title,
-      testSpecificMock,
+      testSpecificMock: mockRequests,
       dapp: true,
       localNodeOptions: {
         hardfork: 'london',