Add some main unittests with standard test runner unittest

[IloBe]

Goal:
Show the behaviour of testing on small components. so, create unittests.

Test Library Usage:
The test runner 'unittests' is chosen, because its library is built into the Python standard library since Python version 2.1.
The library includes the testing framework and the test runner.
The test runner 'pytest' would be another option.

unittest requires that:

• You put your tests into classes as methods
  

• You use a series of special assertion methods in the unittest.TestCase class instead of the built-in assert statement
  

Documentation:
https://docs.python.org/3/library/unittest.html