Optimizing error guessing

When designing your test plan, you need to identify the relevant inputs and variables, considering the partitions and combinations of partitions to test. You need to use your creativity to choose representative cases and examples to try. Be evil! Choose the worst possible examples, the tests that are most likely to cause breakages. What has the development team not thought of? What do they sometimes forget? What broke last time in a feature like this or in this area?

Error guessing is an official title for the ad hoc process of coming up with those test cases. It relies heavily on experience, so, like exploratory testing, it is best suited to experienced testers or those who can think up interesting new cases. Areas with previous errors are prime candidates to test with your new feature. As another of the ISTQB principles states, bugs cluster together and are not evenly spread throughout an application. By knowing about previous clusters, you can make your...