Add new file pytest

python-packages/pytest.yml

+test:
+    tags:
+    - docker  # this is necessary to execute the Gitlab Runner in a docker container
+    image: $ACR_URL/python:3.8
+    only:
+        refs:
+        # run only when new tag is published or changes pushed to master
+        - tags
+        - master
+        - main
+    script:
+        # run test files in tests folder
+        - source $VIRTUALENV_NAME/bin/activate
+        - pip install pytest
+        - pytest tests