[pfdietz]

How do you determine if your tests are good at finding logic errors?

Mutation testing. Introduce artificial logic errors and see if your tests find them.

Disappointed the article didn't go into this. You can even use mutation as part of a test generator, saving the (minimized) first test input that kills a mutant. You still need some way of determining what the right answer was (killing the mutant just involves seeing it does something different from the unmutated program.)