Tests: Shard JS unit tests (#60045)

Split out JS date unit tests
Shard main JS unit tests into 4 shards.

By sharding the tests, they can run in parallel on different runners. This allows the job to complete in less time. Testing suggests the time is reduced by around 50% from 4m to 2m.

Co-authored-by: sirreal <[email protected]>
Co-authored-by: desrosj <[email protected]>

.github/workflows/unit-test.yml

@@ -21,16 +21,18 @@ concurrency:
 
 jobs:
     unit-js:
-        name: JavaScript (Node.js ${{ matrix.node }})
+        name: JavaScript (Node.js ${{ matrix.node }}) ${{ matrix.shard }}
         runs-on: ubuntu-latest
         if: ${{ github.repository == 'WordPress/gutenberg' || github.event_name == 'pull_request' }}
         strategy:
             fail-fast: false
             matrix:
                 node: ['20', '21']
+                shard: ['1/4', '2/4', '3/4', '4/4']
 
         steps:
-            - uses: actions/checkout@9bb56186c3b09b4f86b1c65136769dd318469633 # v4.1.2
+            - name: Checkout repository
+              uses: actions/checkout@9bb56186c3b09b4f86b1c65136769dd318469633 # v4.1.2
               with:
                   show-progress: ${{ runner.debug == '1' && 'true' || 'false' }}
 
@@ -39,20 +41,55 @@ jobs:
               with:
                   node-version: ${{ matrix.node }}
 
-            - name: Get number of CPU cores
+            - name: Determine the number of CPU cores
               uses: SimenB/github-actions-cpu-cores@97ba232459a8e02ff6121db9362b09661c875ab8 # v2.0.0
               id: cpu-cores
 
-            - name: npm build
+            - name: Run build scripts
               # It's not necessary to run the full build, since Jest can interpret
               # source files with `babel-jest`. Some packages have their own custom
               # build tasks, however. These must be run.
               run: npx lerna run build
 
             - name: Running the tests
-              run: npm run test:unit -- --ci --maxWorkers=${{ steps.cpu-cores.outputs.count }} --cacheDirectory="$HOME/.jest-cache"
+              run: |
+                  npm run test:unit -- \
+                    --ci \
+                    --maxWorkers="${{ steps.cpu-cores.outputs.count }}" \
+                    --shard="${{ matrix.shard }}" \
+                    --cacheDirectory="$HOME/.jest-cache"
+
+    unit-js-date:
+        name: JavaScript Date Tests (Node.js ${{ matrix.node }})
+        runs-on: ubuntu-latest
+        if: ${{ github.repository == 'WordPress/gutenberg' || github.event_name == 'pull_request' }}
+        strategy:
+            fail-fast: false
+            matrix:
+                node: ['20', '21']
+
+        steps:
+            - name: Checkout repository
+              uses: actions/checkout@9bb56186c3b09b4f86b1c65136769dd318469633 # v4.1.2
+              with:
+                  show-progress: ${{ runner.debug == '1' && 'true' || 'false' }}
+
+            - name: Setup Node.js and install dependencies
+              uses: ./.github/setup-node
+              with:
+                  node-version: ${{ matrix.node }}
+
+            - name: Determine the number of CPU cores
+              uses: SimenB/github-actions-cpu-cores@97ba232459a8e02ff6121db9362b09661c875ab8 # v2.0.0
+              id: cpu-cores
 
-            - name: Running the date tests
+            - name: Run build scripts
+              # It's not necessary to run the full build, since Jest can interpret
+              # source files with `babel-jest`. Some packages have their own custom
+              # build tasks, however. These must be run.
+              run: npx lerna run build
+
+            - name: Run the date tests
               run: npm run test:unit:date -- --ci --maxWorkers=${{ steps.cpu-cores.outputs.count }} --cacheDirectory="$HOME/.jest-cache"
 
     compute-previous-wordpress-version:
@@ -134,7 +171,8 @@ jobs:
             WP_ENV_CORE: ${{ matrix.wordpress == '' && 'WordPress/WordPress' || format( 'https://wordpress.org/wordpress-{0}.zip', matrix.wordpress ) }}
 
         steps:
-            - uses: actions/checkout@9bb56186c3b09b4f86b1c65136769dd318469633 # v4.1.2
+            - name: Checkout repository
+              uses: actions/checkout@9bb56186c3b09b4f86b1c65136769dd318469633 # v4.1.2
               with:
                   show-progress: ${{ runner.debug == '1' && 'true' || 'false' }}
 
@@ -314,18 +352,19 @@ jobs:
         if: ${{ github.repository == 'WordPress/gutenberg' || github.event_name == 'pull_request' }}
 
         steps:
-            - uses: actions/checkout@9bb56186c3b09b4f86b1c65136769dd318469633 # v4.1.2
+            - name: Checkout repository
+              uses: actions/checkout@9bb56186c3b09b4f86b1c65136769dd318469633 # v4.1.2
               with:
                   show-progress: ${{ runner.debug == '1' && 'true' || 'false' }}
 
-            - name: Get number of CPU cores
+            - name: Determine the number of CPU cores
               uses: SimenB/github-actions-cpu-cores@97ba232459a8e02ff6121db9362b09661c875ab8 # v2.0.0
               id: cpu-cores
 
             - name: Setup Node.js and install dependencies
               uses: ./.github/setup-node
 
-            - name: Npm build
+            - name: Run build scripts
               # It's not necessary to run the full build, since Jest can interpret
               # source files with `babel-jest`. Some packages have their own custom
               # build tasks, however. These must be run.