This solution is for old kata without parenthesis.

If you want to add methods to Array.prototype, make sure they are not enumerable. ( Look up Object.defineProperty on MDN. )

Adding enumerable methods there is not good practice, and I don't blame a test suite for not specifically guarding against that. If you want to use that ( perfectly valid! ) JavaScript feature, do it correctly - or suffer the consequences.

It would really, really help if you post what language you're having this problem with, and ( properly marked up and spoilered ) your code. Help us help you!

Read smolen's and adityavkk's post below, maybe you're adding something to array prototype like them?

No, I didn't. I'd have to change the task to make expected output > input. And all current solutions would be invalid.

How do you mean? Expected output for 0 is -1.

I was having the same problem just use float() in covert stirng do not use int() side_not 8.0 ==8 True

Can an integer have multiple decimals in it? OFC not, so thats where it is coming from.