How does one test a method that does some interactions with the local D-Bus (accessing a HAL object)? 
Results of tests will differ depending on the system that the test is run on, so I don't know how to provide the method reliable input. 
I'm working in Python, by the way.
If you can not mock the environment then it's probably impossible for you to write the test.
If your access to HAL/D-Bus is via an object and you provide a mock instance to your test then it should be possible to emulate the necessary inputs to your test from the mock implementation.
Unit testing for D-Bus and HAL?