Classmates uses only one kind of tests so far: unit-test.

Planned are stress tests (random input ==> see that it works *somehow*, 
no exceptions and so on) and some timing 'tests'.

unit tests
==========

Unit tests have to be self-contained. 

Allowed imports are:
   * anything *outside* classmates,
   * relative imports to "libraries" inside the test directory and
   * the one file that contains whatever where about to test.

If this leads to code duplication, this is the place to do so.
