add Github action to run pytests

.github/workflows/pytests.yaml

@@ -0,0 +1,35 @@
+name: Run pytests
+on: [push, pull_request]
+
+jobs:
+  run_pytests:
+    runs-on: ubuntu-latest
+    name: Install pygw and run tests with pytests
+    strategy:
+      matrix:
+        python: ["3.7", "3.8", "3.9", "3.10"]
+
+    steps:
+      - name: Setup Python
+        uses: actions/setup-python@v3
+        with:
+          python-version: ${{ matrix.python }}
+
+      - name: Install (upgrade) dependencies
+        run: |
+          pip install --upgrade pip
+
+      - name: Checkout
+        uses: actions/checkout@v2
+        with:
+          path: global-workflow
+
+      - name: Install pygw
+        run: |
+          cd $GITHUB_WORKSPACE/global-workflow/ush/python/pygw
+          pip install .[dev]
+
+      - name: Run pytests
+        run: |
+          cd $GITHUB_WORKSPACE/global-workflow/ush/python/pygw
+          pytest -v src/tests