Write tests for the module

I created a MR for this that needs reviews, they have basic tests, including a test that creates two nodes of type article with two different field lists, just to check that the radiostoslider module didn't screw up the site.

Screen:

Needs review (any novice user)?

I'll move it to "Fixed" for now, I plan to create more complex tests in combination with other issues.

I'll close it for now, I'll create some more tests during the development process of this module.

Automatically closed - issue fixed for 2 weeks with no activity.