As noted earlier, usability tests are usually performed with a user interface (UI) simulation rather than an actual product. Such simulations can range from hand-drawn sketches to interactive prototypes that are almost indistinguishable from a real product. The more realistic and interactive simulations generally lead to findings that are more complete and easier to interpret. On the other hand, less time is required to construct simulations that are less realistic or more static, thus allowing for more usability test cycles or a shorter product design stage. For a typical usability test, paper mockups or simple HTML prototypes might be built in 5-10 days, while a highly realistic prototype might require a month -- and more programming skill -- to build. How this trade-off is managed for your project will depend on the availability of programming expertise, the duration of your design stage, and the importance of highly realistic testing or highly efficient interaction.
For purposes of usability testing, it is important that your simulation illustrates at least the sequence of UI states that the user would see if he or she completes the tasks exactly as envisioned by the designer. This makes it possible for participants to show or state what they would do at each step of the task, thus simulating actual task performance.

Beyond the core task steps, navigation options are the next most important thing to illustrate -- particularly the top-level navigation options. For example, if your product includes popup or pulldown menus, provide representations of those menus even if they are not required for the tasks to be performed. This will aid in identifying misleading, ambiguous, or poorly organized navigation options.

Even in highly interactive simulations, many functions of the UI may not be enabled because they are not relevant to the tasks to be tested. If the user selects a function or feature that is not implemented, present a popup message identifying that feature and stating that it is not currently available in the prototype. Clear identification of the feature in the popup message enables observers to readily see which navigation option the user chose.