See this thread for reasoning and acceptance from contributors: https://groups.google.com/d/topic/qubes-devel/G7KzrfU0lWY/discussion "Changing qubes-core-admin license to LGPL v2.1+"
Changed the inheritance hierarchy: 1. Renamed `SystemTestsMixin` to `SystemTestCase` 2. `SystemTestCase` is a child of `QubesTestCase` 3. All classes extending the prior `SystemTestsMixin` now just extend `object`
fixes QubesOS/qubes-issues#2074