Rust: The tests seem to have issues.

I got this compilation error:

error[E0308]: mismatched types
   --> src/lib.rs:129:9
    |
129 |         assert_eq!(partitions(n), size);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `u32`
    |
    = note: this error originates in the macro `assert_eq` (in Nightly builds, run with -Z macro-backtrace for more info)

For more information about this error, try `rustc --explain E0308`.
error: could not compile `challenge` due to previous error


NOTE: Line numbers in error messages can be incorrect due to concatenation.

I suspect the size variable in the test is u32 instead of usize.

Why use isize rather than usize?

Duplicate, as mentioned by @jcsahnwaldt below.