Improve Test Infrastructure (Part 1)

Since quite some time we have some better ways to test functionalities. Instead of just using the return value of ```assert``` we can actually check directly with methods like ```assert_true```, ```assert_false``` and ```assert_raise```. With these we can make the tests more clear and remove lots of helper variables with aren't important to the tests but only to save the test result and validate it later. I started here with to empower the test infrastructure to use these assert methods:

- add assert_not_equal
- add assert_not_include
- Improve undef tests
- Improve alias tests
- Improve the following class depending tests:
ArgumentError, Array, BasicObject, Class, Comparable, Enumerable, Exception, false