feat: Make Jest unit tests run faster in GitHub actions (#25726)

<!--
Please submit this PR as a draft initially.
Do not mark it as "Ready for review" until the template has been
completely filled out, and PR status checks have passed at least once.
-->

## **Description**

<!--
Write a short description of the changes included in this pull request,
also include relevant motivation and context. Have in mind the following
questions:
1. What is the reason for the change?
2. What is the improvement/solution?
-->

[![Open in GitHub
Codespaces](https://github.com/codespaces/badge.svg)](https://codespaces.new/MetaMask/metamask-extension/pull/25726?quickstart=1)

Based on #25680, by
migrating the jest unit tests from CircleCI to GitHub actions the time
to run unit tests has increased to 15 minutes from 5 minutes. This PR
makes Jest unit tests run faster in Github actions. This is achieved by
some improvements to the testing infrastructure.

1. **Sharding**: the tests are run on 6 machines in parallel, instead of
a single machine. This saves around ~8-9 minutes on average.
2. **Optimized coverage generation**: I removed the generation of html
reports in CI, as they are only used for local debugging. This should
also save some time, as unused files are not being generated on CI.
3. **Merged development tests**: The two small tests under
`build/transforms` were merged into the main test configuration. This
means that one less machine needs to be started (as the development
tests would require their own machine to run, due to the sharding
introduced in this PR), saving around approx. 2 minutes of compute time.
4. **Minor fixes**: Now the `run-unit-tests` workflow will also run on
push to the `develop` and `master` branches.

## **Related issues**

Fixes: #25680,

## **Manual testing steps**

1. Run CI and see that tests are running fast (between 5-7 mins on
average)

## **Screenshots/Recordings**

Not Applicable

## **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/develop/.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/develop/.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.

.github/workflows/run-unit-tests.yml

@@ -1,32 +1,52 @@
-# WARNING! It is currently being investigated how to make this faster
-# DO NOT blindly copy this workflow, not noticing the slow down,
-# because suddenly our tests will take hours to pass CI.
-# Hopefully this comment here will help prevent that.
-# https://github.com/MetaMask/metamask-extension/issues/25680
-
 name: Run unit tests
 
 on:
+  push:
+    branches: [develop, master]
   pull_request:
     types: [opened,reopened,synchronize]
 
 jobs:
-  test-unit-jest:
+  test-unit:
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        shard: [1, 2, 3, 4, 5, 6]
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4
 
       - name: Setup environment
         uses: ./.github/actions/setup-environment
 
-      - name: test:coverage:jest:dev
-        run: yarn test:coverage:jest:dev
+      - name: test:unit:coverage
+        run: yarn test:unit:coverage --shard=${{ matrix.shard }}/${{ strategy.job-total }}
+
+      - name: Rename coverage to shard coverage
+        run: mv coverage/coverage-final.json coverage/coverage-${{matrix.shard}}.json
+
+      - uses: actions/upload-artifact@v4
+        with:
+          name: coverage-${{matrix.shard}}
+          path: coverage/coverage-${{matrix.shard}}.json
+
+  report-coverage:
+    runs-on: ubuntu-latest
+    needs:
+      - test-unit
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
 
-      - name: test:coverage:jest
-        run: yarn test:coverage:jest
+      - name: Download coverage from shards
+        uses: actions/download-artifact@v4
+        with:
+          path: coverage
+          pattern: coverage-*
+          merge-multiple: true
 
-      - uses: codecov/codecov-action@e28ff129e5465c2c0dcc6f003fc735cb6ae0c673
+      - name: Upload coverage to Codecov
+        uses: codecov/codecov-action@e28ff129e5465c2c0dcc6f003fc735cb6ae0c673
         with:
           token: ${{ secrets.CODECOV_TOKEN }}
           fail_ci_if_error: true

development/build/transforms/remove-fenced-code.test.js

@@ -1,3 +1,6 @@
+/**
+ * @jest-environment node
+ */
 const buildUtils = require('@metamask/build-utils');
 const { createRemoveFencedCodeTransform } = require('./remove-fenced-code');
 const transformUtils = require('./utils');
@@ -36,6 +39,10 @@ describe('build/transforms/remove-fenced-code', () => {
       lintTransformedFileMock.mockImplementation(() => Promise.resolve());
     });
 
+    afterEach(() => {
+      jest.resetAllMocks();
+    });
+
     it('returns a PassThrough stream for files with ignored extensions', async () => {
       const fileContent = '"Valid JSON content"\n';
       const stream = createRemoveFencedCodeTransform(

development/build/transforms/utils.test.js

@@ -1,3 +1,6 @@
+/**
+ * @jest-environment node
+ */
 const { getESLintInstance } = require('./utils');
 
 let mockESLint;

jest.config.js

@@ -3,10 +3,11 @@ module.exports = {
     '<rootDir>/app/scripts/**/*.(js|ts|tsx)',
     '<rootDir>/shared/**/*.(js|ts|tsx)',
     '<rootDir>/ui/**/*.(js|ts|tsx)',
+    '<rootDir>/development/build/transforms/**/*.js',
   ],
   coverageDirectory: './coverage',
   coveragePathIgnorePatterns: ['.stories.*', '.snap'],
-  coverageReporters: ['html', 'json'],
+  coverageReporters: process.env.CI ? ['json'] : ['html', 'json'],
   reporters: [
     'default',
     [
@@ -26,7 +27,7 @@ module.exports = {
     '<rootDir>/app/scripts/**/*.test.(js|ts|tsx)',
     '<rootDir>/shared/**/*.test.(js|ts|tsx)',
     '<rootDir>/ui/**/*.test.(js|ts|tsx)',
-    '<rootDir>/development/fitness-functions/**/*.test.(js|ts|tsx)',
+    '<rootDir>/development/**/*.test.(js|ts|tsx)',
     '<rootDir>/test/e2e/helpers.test.js',
   ],
   testTimeout: 5500,

package.json

@@ -38,12 +38,12 @@
     "dapp-chain": "GANACHE_ARGS='-b 2' concurrently -k -n ganache,dapp -p '[{time}][{name}]' 'yarn ganache:start' 'sleep 5 && yarn dapp'",
     "forwarder": "node ./development/static-server.js ./node_modules/@metamask/forwarder/dist/ --port 9010",
     "dapp-forwarder": "concurrently -k -n forwarder,dapp -p '[{time}][{name}]' 'yarn forwarder' 'yarn dapp'",
+    "test:unit": "jest",
+    "test:unit:watch": "jest --watch",
+    "test:unit:global": "mocha test/unit-global/*.test.js",
+    "test:unit:coverage": "jest --coverage",
     "test:integration": "jest --config jest.integration.config.js",
     "test:integration:coverage": "jest --config jest.integration.config.js --coverage",
-    "test:unit": "node ./test/run-unit-tests.js --jestGlobal --jestDev",
-    "test:unit:jest": "node ./test/run-unit-tests.js --jestGlobal --jestDev",
-    "test:unit:jest:watch": "node --inspect ./node_modules/.bin/jest --watch",
-    "test:unit:global": "mocha test/unit-global/*.test.js",
     "test:e2e:chrome": "SELENIUM_BROWSER=chrome node test/e2e/run-all.js",
     "test:e2e:chrome:mmi": "SELENIUM_BROWSER=chrome node test/e2e/run-all.js --mmi",
     "test:e2e:chrome:flask": "SELENIUM_BROWSER=chrome node test/e2e/run-all.js --build-type flask",
@@ -61,10 +61,6 @@
     "test:e2e:firefox": "SELENIUM_BROWSER=firefox node test/e2e/run-all.js",
     "test:e2e:firefox:flask": "SELENIUM_BROWSER=firefox node test/e2e/run-all.js --build-type flask",
     "test:e2e:single": "node test/e2e/run-e2e-test.js",
-    "test:coverage:jest": "node ./test/run-unit-tests.js --jestGlobal --coverage",
-    "test:coverage:jest:dev": "node ./test/run-unit-tests.js --jestDev --coverage",
-    "test:coverage": "node ./test/run-unit-tests.js --jestGlobal --jestDev --coverage",
-    "test:coverage:html": "yarn test:coverage --html",
     "ganache:start": "./development/run-ganache.sh",
     "sentry:publish": "node ./development/sentry-publish.js",
     "lint": "yarn lint:prettier && yarn lint:eslint && yarn lint:tsc && yarn lint:styles",