Update test code for python 3

[KazuCocoa]

Current test code inherits object and can make them more pytest style.
#636 (comment)

[navin772]

Hi @KazuCocoa, what else needs to be changed apart from removing inheritance of the object?

[KazuCocoa]

The syntax related is the object. I think we have more minor things, but I don't have concrete examples right now.