Add github workflow

.github/workflows/test.yml

@@ -0,0 +1,33 @@
+name: Pytests
+
+on: [push, pull_request]
+
+jobs:
+  test:
+    name: Tests
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ["3.6", "3.7", "3.8", "3.9"]
+    steps:
+    - name: Check out
+      uses: actions/checkout@v2
+    - name: Set up Python ${{ matrix.python-version }}
+      uses: actions/setup-python@v2
+      with:
+        python-version: ${{ matrix.python-version }}
+    - name: Install pip dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install .
+        pip install .[columns]
+        pip install .[ical]
+        pip install .[prompt]
+        pip install .[test]
+        pip install pylint
+        pip install codecov
+        pip install -U isort
+        pip install pytest
+    - name: Run pytests
+      run: |
+        python -m pytest