Add tests

[misteu]

Goal
The code should be tested.

AC
Do not add any 3rd party testing frameworks only use XCTest.

Current State
There aren't any tests yet.

[codewithnadeem14502]

hello sir/mam, i want to contribute to it, can you assign me this issue and i am completely new to open source

[misteu]

Hello,
thanks for your interest. Please have a look at my questions here in the other issue you were interested: #1 (comment)