I have the same issue (JavaScript), all my tests pass and I'm checking if the move is out of bounds.

It's difficult without seeing your code. But from other people's problems, my guess is that your code has problems with the following test:

isMerge('aaba', 'aa', 'ab') which should equal true since:

s:     a a b a
part1: a     a
part2:   a b

Maybe that will nudge you in the right direction.

If not, I'd be happy to take a peek at your code and give some hints.

Good luck! :-)

The simple tests work but the others don't, can't figure out what's the issue :/