Has anyone created a program to test another program?

For example, say you have a simple database program and you want to test user input/create records. Instead of sitting their monotonously testing it yourself, you could use this other program to "simulate" the testing (create records etc). This other program would work just like a user (no shortcuts or tricks), except it does the work itself.

I suppose you could design your Test Plan and then use that as a Requirements Definition for a second Program. How would you test it though ? :)

Google automated testing tool for some possibilities. I don't know of any free tools and a lot are browser/Web oriented but you never know what might be out there.