Added 'CI' GitHub action

Runs pytest and black lint

.github/workflows/ci.yml

@@ -0,0 +1,18 @@
+name: CI
+
+on: [push, pull_request]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - name: Set up Python
+      uses: actions/setup-python@v5
+      with:
+        python-version: '3.x'
+    - name: Test with pytest
+      run: |
+        pip install pytest black 
+        pytest 
+        black --check --line-length 79 .