shift to Characterization test

• I have to make the unit test for the classes someone made.
• I have been studying the classes and making the unit tests for them simultaneously.
• Some class files have the examples of use in the comment statements

This is why I will start to make the tests with Characterization test until now.

Basically, I will prepare a test class for a class, and test the behaviors for the methods.

I won't write tests for private methods. I will write them only for methods that can be accessed externally.

However, even if they are private methods, they should pass C0 test.(I will manage it with rcov.)