Add code coverage

codecov.yml in github workflows. Adapted from https://wkrzywiec.medium.com/how-to-write-good-quality-python-code-with-github-actions-2f635a2ab09a

.github/workflows/codecov.yml

@@ -0,0 +1,27 @@
+name: Codecov workflow
+on:
+  push:
+    branches:
+      - 'master'
+jobs:
+  codecov:
+    name: Codecov Workflow
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v1
+      - name: Set up Python
+        uses: actions/setup-python@master
+        with:
+          python-version: 3.8
+      - name: Generate coverage report
+        run: |
+          pip install pytest
+          pip install pytest-cov
+          pytest --cov=./ --cov-report=xml
+      - name: Upload coverage to Codecov
+        uses: codecov/codecov-action@v1
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }}
+          file: ./coverage.xml
+          flags: unittests