For some reason Codewars submitted an unrefactored version of this solution. The final version of this is very different and removes a lot of the unnecessary elements in this version.

A fantastic kata, one of the best!!

That is my point, except that "N/A or an infinite number of years" in this case means an infinite loop, causing the application to freeze. This would not be best practices, as over 100 votes have claimed.

If invalid input is given to this method, it doesn't indicate it by either a returned value or an exception; instead, it just never returns at all.

That is what my question was trying to illuminate: if tax is not less than 1 or if interest is not greater than 0, what happens is a frozen application.

323 = 17 * 19

What will happen if Tax is not less than 1 or if interest is not greater than 0?