TEString unit tests

[aregtech]

Motivation
The string class is one of the most used class. We need unit tests to check and optimize the methods.

Actions

• Similar to NEString, there should be unit tests written to test string operations.
• During unit tests, make measurements and optimize the operations.
• The unit tests should include as much variations as possible.

Additional actions:
Fix the bugs during unit test implementation.

[biwiki]

@aregtech am wondering if you have started on this by any chance?

[aregtech]

I was doing, but didn't complete yet.
In reality, this unit test is big, and definitely makes sense to split. And most probably I'll find some bugs :)
Any help, of course always welcomed.