[Feature]: Add a testing framework

[Laurick]

Description

In order to be VST a "production ready" addon we need tests

Current Behavior

There is no test framework neither testing suite

How

Gut seems to be a good testing famework ( https://gut.readthedocs.io/en/latest/ ) The idea is to add the framework as first step with a dummy test. The next step will be a series of small refactors to extract methods and test them

It's seems also we can attach it to PRs in order to keep the project robust and merge only the "safe" ones

[rothiotome]

I didn't know GUT but seems like a goood option to add tests to the project. We can investigate it further in the following weeks