Switch to pytest for Python unit tests CI

- Use pytest to run unit tests in the GitHub Actions workflow
- Add a pytest configuration file

Author: per1234

.github/workflows/libraries_report-size-deltas.yml

@@ -15,6 +15,11 @@ jobs:
         with:
           python-version: '3.8.2'
 
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install --requirement "$GITHUB_WORKSPACE/libraries/report-size-deltas/requirements.txt"
+
       - name: Lint with flake8
         run: |
           pip install --quiet flake8
@@ -24,4 +29,4 @@ jobs:
       - name: Run Python unit tests
         run: |
           export PYTHONPATH="$GITHUB_WORKSPACE/libraries/report-size-deltas"
-          python -m unittest discover "$GITHUB_WORKSPACE/libraries/report-size-deltas/tests"
+          pytest "$GITHUB_WORKSPACE/libraries/report-size-deltas/tests"

requirements.txt

@@ -0,0 +1 @@
+pytest==5.4.1

tests/pytest.ini

@@ -0,0 +1,8 @@
+[pytest]
+filterwarnings =
+    error
+    ignore::DeprecationWarning
+    ignore::ResourceWarning
+
+markers =
+    slow: marks tests as slow (deselect with '-m "not slow"')