[WIP] Add module for writing unit tests

[podocarp]

Description

Usually testing of programs in source academy is done by commenting and uncommenting code. This is a great big hassle. I have also noticed that students usually only run a single test at a time and comment/uncomment
every single line manually, which makes it even slower. Thus it would be great if we could introduce proper unit testing into Source.

This module adds a few function for writing tests and asserts, as well as a new tab to report on test statuses.

I have generally tried to keep to a style similar to jest.

Future extensions:

• Compare runes, sound, etc.
• Style the tab a bit nicer

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Added unit tests, as well as manual testing.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[Anonymxtrix]

Great job! I think that this test module that you have written will definitely be a hit among the source academy cadets! Too bad this wasn't yet implemented when I was taking 1101s haha.

The comments I added are generally my opinion (pls don't take any offence) and feel free to contact me if you wish to discuss or argue against any of the points I wrote so that we can learn together as well! :)

[martin-henz]

This PR is still marked as "draft". @podocarp: Or is it ready for final review?

[podocarp]

Have not written docs yet, but hope someone can look at the code first.