Iterative testing is natural for the projects when interfaces can hardly be evaluated by an expert assessment — e.g. for brand new products or sophisticated subject area. Testing with real users during design stage allows to check the all the proposed solutions and to get a prototype that fully suits user tasks. We create UI prototypes with lots of interactivity and content that just looks real, so that interface solutions may be tested, and potential problems may be revealed during the design phase.
Combining this approach with the rapid prototyping approach allows to introduce changes in a fast and easy manner.