Aside from differences in goals and types of data sought, usability tests also vary as to formality and scope of coverage, as are discussed here.
The rigor and formality of usability tests vary widely. Comparative tests must be planned and conducted very carefully to produce valid results. The design, execution, and analysis of such studies require a solid understanding of experimental design. At the other extreme might be an informal "walkabout" study, using paper mockups that show several consecutive states of a software user interface that supports a particular task. The test administrator walks through an office building looking for unsuspecting personnel loitering at water fountains or staring blankly at their screensavers. In ten minutes time, a participant is recruited and has attempted the task, observations have been jotted on a steno pad, and the test administrator has turned his or her gaze toward the next underutilized employee.

A usability test, or even a series of usability tests, rarely if ever tests all capabilities of a product. A typical usability test focuses on the most common or most important tasks because such tasks are most pivotal to the success of the product. For a software design employing a new navigational framework, a usability test might also be designed to exercise each of the framework features. As the usability characteristics of a design become better understood, follow-on studies are aimed at evaluating proposed solutions to previously observed problems and at testing less common tasks that seem to pose a usability risk.