docs: Add Parallel Test Example

README.md

@@ -23,6 +23,8 @@ on:
 jobs:
   rspec:
     steps:
+      # setup...
+
       - name: Test
         run: bundle exec rspec -f j -o tmp/rspec_results.json -f p
 
@@ -33,3 +35,63 @@ jobs:
           json-path: tmp/rspec_results.json
         if: always()
 ```
+
+## Parallel Test Example
+```yaml
+name: Build
+on:
+  pull_request:
+
+jobs:
+  rspec:
+    strategy:
+      fail-fast: false
+      matrix:
+        ci_node_index: [0, 1]
+        ci_node_total: [2]
+    steps:
+      # setup...
+
+      # Recommend using `r7kamura/split-tests-by-timings`.
+      - id: split-tests
+        run: |
+          PATHS=$(
+            find spec -type f -name '*_spec.rb' | \
+              xargs wc -l | \
+              head -n -1 | \
+              sort -n | \
+              awk -v node=${{ matrix.ci_node_index }} -v total=${{ matrix.ci_node_total }} 'NR % total == node {print $2}' | \
+              tr '\n' ' '
+          )
+          echo "paths=$PATHS" >> "$GITHUB_OUTPUT"
+        shell: bash
+
+      - name: Test
+        run: |
+          bundle exec rspec \
+            -f j -o tmp/json-reports/rspec_results-${{ matrix.ci_node_index }}.json \
+            -f p \
+            ${{ steps.split-tests.outputs.paths }}
+      - uses: actions/upload-artifact@v4
+        with:
+          if-no-files-found: error
+          name: json-reports-${{ matrix.ci_node_index }}
+          path: tmp/json-reports
+        if: always()
+
+  report-rspec:
+    needs: rspec
+    if: always()
+    steps:
+      - name: Download all rspec results
+        uses: actions/download-artifact@v4
+        with:
+          pattern: json-reports-*
+          path: /tmp/json-reports
+          merge-multiple: true
+      - name: RSpec Report
+        uses: SonicGarden/rspec-report-action@v4
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          json-path: /tmp/json-reports/rspec_results-*.json
+```