Analyse code coverage in tests

By analysing the code coverage in the test files, we can make sure that we do not accidentially remove a test
and that all test code actually is used

tox.ini

@@ -12,7 +12,7 @@ deps =
     coverage
     hypothesis
 commands =
-    coverage run --source=src/icalendar --omit=*/tests/* --module pytest []
+    coverage run --source=src/icalendar --omit=*/tests/hypothesis/* --omit=*/tests/fuzzed/* --module pytest []
     coverage report
     coverage html