Thankyou for helping me out. As a beginner these nudges to the right direction help a lot.

Congratulations to the 200th post for this kata. :-)

If you changed that if, you probably got the wrong answer on the last if instead. Neither remString nor remString2 will change from their initial values.

(Btw. That last if-statement will result in a a false negative for isMerge("aaaa", "aa", "aa") as well, so you might need to rethink your strategy.)

I did try that earlier and it did not work, just to see if it works i changed the if, so basically it expects false for all of them except the last 0 + 0 = 0 case

Well, an empty string can absolutely be the merge of two empty strings. Just like 0 + 0 = 0. I haven't gone through the whole code, but the first if-statement looks suspicious.

Good luck! :-)