Added test_load_basic

[dtomci]

Hello, so here is the test for load_basic. Hopefully its somewhat correct and what you expected.

[MyreMylar]

It should be OK to actually call load_basic() in this test for now, we are discouraging the use of load_basic() in the documentation but for the unit test it makes sense to call it directly. I know load() redirects to load_basic() but that's why we have tests for load() too :)

Other things that could be tried is loading an actual file from the examples data directory e.g.:

load_basic(example_path("data/asprite.bmp"))

and perhaps loading from a file-like object like io.BytesIO?