Add Testing Framework

[BradyAJohnston]

So far I have been slack on introducing formal unit testing & CI, as it's slightly more complex when having to try and test inside of Blender, which is a desktop app and not a installable package.

I have found the blender-addon-tester which aims to solve such a problem by scraping the Blender downloads page for relevant versions, downloading them then running Blender in the headless mode to run various pytest tests.

Certainly the import code should be able to be tested with this method, and reported on with pytest. The testing of the internal nodes will be slightly more difficult. In conversation with Blender devs, saving a 3D model and comparing it to a previously created 3D model is their method of testing the nodes, so potentially will try and set up something along those lines. .gltf is likely the model of choice.

This PR introduces the testing framework, which I am looking to add some more initial tests to in the coming weeks.

[codecov]

Codecov Report

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Additional details and impacted files

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[BradyAJohnston]

Using more robust testing in #186