Implement basic tests for the core modules.

[nandorholozsnyak]

Description
A library is only considered stable and rock solid if it has been tested well, please implement basic unit tests for the different scenarios.

TODO:

• Tests for the response example documenter.
• Tests for the request body example documenter.

[nandorholozsnyak]

Small tests were introduced, more needed to fulfill the gaps and the coverage.