An equivalence class is a set of tests that test the same thing. All tests in an equivalence class expose the same bugs. Whenever I test an application, I use equivalence classes to help choose what data and conditions to exercise under test. It provides good test coverage while reducing the number of test cases.

 

I use mind maps to visually represent equivalence classes so I can decide where to focus my testing. Normally I try to identify as many classes as I can, and then, depending on how much effort I choose to invest, I select the equivalence classes that offer me the most value as a tester.

I use a three-step approach to create a mind map for an equivalence class:

• Identify the variables.

• Identify classes based on application logic, input, and memory (AIM).

• Identify invalid classes.