Add basic test for the AllocationTrackerClassFileTransformer

This PR adds a very basic test for the ```AllocationTrackerClassFileTransformer```. It checks
- whether classes from the tracker packer are ignored
- whether classes with the wrong prefix are ignored
- whether the byte representation of classes are changed by the transformer
something that could be easily recognized in byte form. but that would depend on the test. like you said above: check length and start from there.