But if you don't tell the candidate what to do, how do you know if the candidate can do that or not? Most programming exercises that companies use in interview

But if you don't tell the candidate what to do, how do you know if the candidate can do that or not? Most programming exercises that companies use in interviews are much simpler (trivial really) than actual software projects, and personally I don't see the need to write 1 page of documentation and unittests for code that can fit on 3 pages... Does that mean I'm against documentation and can't write unittests? No, I'm simply being pragmatic.