Thanks for the help.
modified the tests, remove all Option and ... submited !
Thanks.

Yes as requested by the tests :

Ok(...)
Except for negative input, returns None.

"Test" is ok.
"Attempt" is not.

tests ok, even fact(800)...
But when attempt :

error[E0277]: can't compare String with Option<String>
--> src/lib.rs:131:26
|
131 | assert!(expected == actual, "For number {num}\nExpected:\n{expected:?}\nActual:\n{actual:?}");
| ^^ no implementation for String == Option<String>
|

Rust tests are not ok.

seconds % 3600 % 60 could be only
seconds % 60