Add a first testing workflow

.github/workflows/testing.yml

@@ -0,0 +1,17 @@
+name: Testing workflow
+
+on: [push, pull_request]
+
+jobs:
+  style:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-python@v2
+        with:
+          python-version: '3.8.10'
+      - name: "Install style checker"
+        run: pip install black
+      - name: "Run style check"
+        run: black --check .
+