Mapping dependent and independent variables

Glaring bugs that happen under a wide range of circumstances are easy to find, even with exploratory testing. If the Logout button never works, you will see that the first time you log out. However, if it usually works but only fails on a certain web browser, a certain browser version, or only after you have changed the browser window size, you might not find the issue. If you don’t test those situations, the Logout button will work in your test. Bugs that only occur under certain circumstances, are much harder to find: you can do X, and you can do Y, but you can’t do X and Y together.

Bugs that depend on multiple variables are challenging to find because the test plan you need is huge. First, you have to identify the variables affecting your system. Some essential variables will have far-reaching effects, such as the operating system you’re running on or the web browser you are using. Those are common, but also consider...