The two things I can think of both have to do with your environment:

1. You don't have permission to write to that folder (ie your script isn't running as the user you think it is)
2. The current working directory is different from what you think it is, so testcron.txt is being created (or not if you don't have permissions), but not in the place where you expect

Try running a simple cron command like: env && pwd > /home/monkfan/test.txt

Clint