This is referred to as the "Wizard of Oz" method (or "experimenter-in-the-loop"). It's very common in HCI research, as well as in product prototyping in various

This is referred to as the "Wizard of Oz" method (or "experimenter-in-the-loop"). It's very common in HCI research, as well as in product prototyping in various industries. https://en.wikipedia.org/wiki/Wizard_of_Oz_experiment https://en.wikipedia.org/wiki/Wizard_of_Oz_experiment A variation of the technique is also common in CS user studies, where the novel tool under study works, but is too computationally intensive (i.e. slow) to actually use in the study. In this variation, the tool's results are precomputed, and the tool's interface is mocked up so that it just retrieves precomputed results (or it delegates to a human researcher playing the "wizard").