More often than not this is down to a technique called ‘Error Guessing’. To be successful at Error Guessing, a certain level of knowledge and experience is required. A Tester can then make an educated guess at where potential problems may arise. This could be based on the Testers experience with a previous iteration of the software, or just a level of knowledge in that area of technology. This test case design technique can be very effective at pin-pointing potential problem areas in software. It is often be used by creating a list of potential problem areas/scenarios, then producing a set of test cases from it. This approach can often find errors that would otherwise be missed by a more structured testing approach.
