Add test coverage report

.github/workflows/build.yaml

@@ -25,13 +25,18 @@ jobs:
 
       # We have two cores so we can speed up the testing with xdist
       - name: Install xdist and openfiles
-        run: pip install pytest-xdist pytest-openfiles pytest-flake8
+        run: pip install pytest-xdist pytest-openfiles pytest-flake8 pytest-cov
 
       - name: Build and install
         run: pip install -v .
 
       - name: Run tests
-        run: pytest -r a -v -n 3 --open-files
+        run: pytest -r a -v -n 3 --open-files --cov=astro_metadata_translator --cov=tests --cov-report=xml --cov-report-term --cov-branch
+
+      - name: Upload coverage to codecov
+        uses: codecov/codecov-action@v2
+        with:
+          file: ./coverage.xml
 
       - name: Install documenteer
         run: pip install -r doc/requirements.txt