This statement is wrong.

When you import circles in the test file (even if you only select circles_area) the circles file basically gets executed from top to bottom to run all definitions at the point of the import statement. This executes your for loop which fails, and the actual tests are never run. Just remove that loop in the circles module, and it should work.

Huh? Hexagonal Architecture?

Jon Gjengset on Youtube is doing live coding where he uses neovim quite well. And you’ll learn about Rust while you’re at it.