build: try matrix for split unit tests

Author: chingor13

.github/workflows/ci.yaml

@@ -45,6 +45,49 @@ jobs:
       env:
         JOB_TYPE: test
         JOB_NAME: units-${{matrix.java}}
+  # detect which libraries have changed
+  changes:
+    runs-on: ubuntu-latest
+    permissions:
+      pull-requests: read
+    outputs:
+      packages: ${{ steps.filters.outputs.changes }}
+    steps:
+    - uses: dorny/paths-filter@v4
+      id: filter
+      with:
+        filters: |
+          java-bigquery: java-bigquery
+          java-bigquerystorage: java-bigquerystorage
+          java-datastore: java-datastore
+  split-units:
+    runs-on: ubuntu-latest
+    needs: changes
+    strategy:
+      fail-fast: false
+      matrix:
+        java: [11, 17, 21, 25]
+        package: ${{ fromJSON(needs.changes.outputs.packages) }}
+    steps:
+    - name: Get current week within the year
+      id: date
+      run: echo "::set-output name=week_of_year::$(date +'%W' --utc)"
+    - uses: actions/checkout@v4
+    - uses: actions/setup-java@v4
+      with:
+        distribution: temurin
+        java-version: ${{matrix.java}}
+    - run: java -version
+    - uses: actions/cache@v4
+      id: mvn-cache
+      with:
+        path: ~/.m2/repository
+        key: ${{ runner.os }}-maven-unified-${{ steps.date.outputs.week_of_year }}
+    - run: .kokoro/build.sh
+      env:
+        BUILD_SUBDIR: ${{matrix.package}}
+        JOB_TYPE: test
+        JOB_NAME: units-${{matrix.package}}-${{matrix.java}}
   windows:
     runs-on: windows-latest
     steps: