Add tests to the extension

[Malacath-92]

The extension starts having enough features that a set of tests is appropriate.
I think some tests will need user interaction to be verified, but many modules could be tested automatically.
It would still be a significant amount of work, though worth it to prevent regression (which we have suffered from a couple of times in the past)

[Malacath-92]

Some tests are added for low level functionality, namely some parsing functionality.
But we should also add some sort of integration tests to make sure that correct type shaders are generated.