(OP was attempting in Rust) is_numeric() returns true for non-ASCII numeric codepoints such as '¾'

isNaN() is not the right tool for the job (or for almost any job for that matter):

isNaN(' ') // false

Thanks for this kata! I enjoyed working through it and refining my own approach — it was a nice balance of thinking and implementation. Really appreciate the effort you put into designing it.

it failing on input '1234\n' but it should not because after creating positive num regex I am not strpie the input.
it should pass the test case, but I am getting fail.

You're not testing it in your system with the same input value. Check the error message again, where the closing quote is, it's in the next line.

I am not sure why it fails, but it succeed on my system checking the same code with same inputs, is there a bug or issue.
Input is `123 ', expected true to equal false,
it actually returns a false, but why the test suite fail.

Not a suggestion?

finish

why can not r'^\d{4}$' cut off \n? May I ask if anyone can answer this？

Description should be language-agnostic (regarding the function name in examples) It should be generalized to just with input and output

Haskell translation

It seems reasonable to rank anything to do with regular expressions as at least 7. It's a whole language within a language.