Improvement of tests

Check existing test cases

• SingleListVariantIncrementalVariantTest
  • currently skipped
  • should be renamed (remove one "Variant")

More test cases

Add more tests, e.g., for:

• inherited attributes
• collection attributes
• circular attributes
• non-terminal lists
• non-terminal opts
• endpoints, that always apply (i.e., do not check for equal content)

Check if non-cached attributes marked with a send endpoint create problems

Better test performance

• Investigate possibility of parallelizing tests
• Reduce wait time (for mqtt). Idea: Add subscriber listening to all topics, and wait only until expected messages arrive. Check at end on total expected messages (maybe add a final wait there)