There is more to the extension than meets the eye through the regular use. Some elements, and some screens, have various special states they can be found in under special circumstances. These are:
We should know which elements can go into error mode. Mostly it will be inputs, drop downs, and similar elements. During testing we need to provoke the extension into making an error in order to check how do the error states manifest in the UI.
Most pages will have a state when all of the data that is usually there is not present. A completely empty Requirements Gathering extension with no projects started. Page Map with no pages to display. We should check are those pages well designed, and is their behaviour OK.