How do you tell that your unit tests are correct?

Question

I\'ve only done minor unit testing at various points in my career. Whenever I start diving into it again, it always troubles me how to prove that my tests are correct. How

Answer 1

Well, Dijkstra famously said:

"Testing shows the presence, not the absence of bugs"

IOW, how would you write a unit test for the function add(int, int)?

IOW, it's a tough one.