the dbusproperties proxy is created by and used by the modem object and that class has it is own set of unit tests to confirm the proxy is created and used correctly modemmanager s unit tests need to confirm only that the modem  init is called  it does that by making sure the task factory  is not empty after the call  we could go a step further and run the event loop but seems redundant  ideally  we would peek into the factory or the even loop and confirm that the pending task is inittask 