Remove unnecessary test

Tunit::Test is a perfect example on how this works
Move dummy_reporter to RunnableTest

It does not need to be accessible through TestCase
Clear out Runnable.runnables after each testrun

Each test should be able to setup its own world before each run
Clarity before cleverness. Always

`NotImplementedError` is a bit unclear in this use-case.
Set the expected assertion count incited of incrementing
Split up assertions from the rest of the tests part ii