Test written files are valid calendars

tests/test_write.py

@@ -2,6 +2,8 @@
 import sys
 from pathlib import Path
 
+import icalendar
+
 from calmerge.config import Config
 
 
@@ -20,4 +22,8 @@ def test_write_config(tmp_path: Path, config: Config, config_path: Path) -> None
     assert len(list(tmp_path.glob("*.ics"))) == len(config.calendars)
 
     for calendar_config in config.calendars:
-        assert tmp_path.joinpath(f"{calendar_config.slug}.ics").is_file()
+        calendar_path = tmp_path.joinpath(f"{calendar_config.slug}.ics")
+        assert calendar_path.is_file()
+
+        calendar = icalendar.Calendar.from_ical(calendar_path.read_text())
+        assert not calendar.is_broken