To be clear, Pega Unit only has native support for the rules mentioned above, however it is also possible to test additional rule types by using a wrapper activity rule. Eventually there will be more rule types that are supported natively for unit testing.
Try to keep making the distinction between 'unit testing' and 'test automation'. Unit testing is ALWAYS possible. It's a mental process of challenging the rules that you configured. PegaUnit is a framework for test automation. Out-of-the-box test automation is supported for the rules mentioned earlier.