Add parallel testing demo

Author: chingc

.github/workflows/parallel.yml

@@ -54,10 +54,10 @@ jobs:
     runs-on: ubuntu-latest
     needs: collect
 
-    strategy:
-      matrix:
-        test_dir: ["tests", "tests/dir1", "tests/dir2", "tests/dir3"]
-        # test_dir: "${{ needs.collect.outputs.TEST_MATRIX }}"
+    # strategy:
+    #   matrix:
+    #     test_dir: ["tests", "tests/dir1", "tests/dir2", "tests/dir3"]
+    # test_dir: "${{ needs.collect.outputs.TEST_MATRIX }}"
 
     steps:
       - uses: actions/checkout@v4
@@ -72,5 +72,7 @@ jobs:
           uv sync --locked; echo
           uv tree
 
-      - name: Run test
-        run: uv run -- pytest '${{ matrix.test_dir }}'
+      # - name: Run test
+      #   run: uv run -- pytest '${{ matrix.test_dir }}'
+
+      - run: echo "TEST_MATRIX is '${{ needs.collect.outputs.TEST_MATRIX }}'"