[TEST] Enforce type hints with MyPy

[jeertmans]

What

In par with #34, I'd like to have some checks to assert that all functions, methods, and constants have type hints.

How to

This PR requires adding a pre-commit hook that using mypy. After the flake8 hook:

manim-slides/.pre-commit-config.yaml

Lines 22 to 30 in 14a266b

	- repo: https://github.com/PyCQA/flake8
	rev: 5.0.4
	hooks:
	- id: flake8
	additional_dependencies:
	- flake8-bugbear
	- flake8-comprehensions
	- flake8-tidy-imports
	- flake8-typing-imports

you need to add:

-   repo: https://github.com/pre-commit/mirrors-mypy
    rev: ''  # Use the sha / tag you want to point at
    hooks:
    -   id: mypy

and use customized arguments to make sure it only checks for type hints.

Useful links

• Using mypy's pre-commit hook
• How to force type hint with mypy

[elliotwutingfeng]

Let me try this

[jeertmans]

Hi @elliotwutingfeng! Sure, go on ;-)
Do not hesitate to ask questions if you have any!