Modify pytest command to run tests individually

Run tests independently to enable tests over spark sessions.

Author: ohamz

.github/workflows/python-app.yml

@@ -38,4 +38,7 @@ jobs:
         flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
     - name: Test with pytest
       run: |
-        pytest
+        # run tests independently to enable tests using spark session
+        for f in tests/test_*.py; do
+          pytest -q "$f" || exit 1
+        done