Add tests for the writer

Author: vanous

.github/workflows/run-tests.yaml

@@ -15,6 +15,8 @@ jobs:
         with:
           timezoneLinux: "Europe/Berlin"
       - uses: actions/checkout@v4
+      - name: Install xmllint
+        run: sudo apt-get update && sudo apt-get install -y libxml2-utils
       - name: Set up Python ${{ matrix.python-version }}
         uses: actions/setup-python@v4
         with: