Once the ideal paths have been tested, focus on secondary paths involving the lower-level functions or actions and steps that are less frequent but still reasonable variations. Forcing errors comes later, if you have time. First Intrinsic factors are those factors or characteristics that are part of the system or product being tested. An intrinsic factor is an internal factor. The code logic called by a submit button is intrinsic to the site.
Extrinsic factors are external to the site or application.
Your crappy computer with only 8 megs of RAM is extrinsic to the site, so your home computer can crash without affecting the commerce site, and adding more memory to your computer doesn't mean a whit to the commerce site or its functioning. The point here is that with myriad possible client configurations and user-defined environmental factors to think about, think first about those that relate to the product or application itself. When you run out of time, better to know that the system works rather than that all monitor resolutions safely render the main pages. Boundary Test From Reasonable to Extreme You can't just verify that an application works correctly if all input and all actions have been correct. People do make mistakes, so you must test error handling and error states.