I don't know if the tests for this are broken or if I made a mistake, but something is wrong. The code I wrote inside a different text editor works great and gives me the expected years when I checked it against the test cases. However, when I run it through the codewars editor, the tests come back undefined. Can anyone help? Here's my code:

var years = 0;
function calculateYears(principal, interest, tax, desired) {
if(principal < desired){
var interestEarned = principal * interest;
var taxAmount = interestEarned * tax;
var net = interestEarned - taxAmount
principal += net;
years ++;
calculateYears(principal, interest, tax, desired)
}else{
return years
}
}