Add MaxHeap unit tests

[Barsonax]

Summary

Add unit tests for the following functionality:

• RemoveFirst
  • add some items to the heap and check if RemoveFirst returns these in the correct order.
• Contains
  • Add some items and check if contains returns true.
  • Add some items and create new items and check if it now returns false for these new items.

[Barsonax]

Implemented on develop