This article explains the why, when, what, how, where, and who of user testing for mobile friendly websites or apps. The sooner you find out your what is wrong with your *brilliant* concept, the easier, quicker, cheaper (and less embarrassing) it is to put it right or – if it is a total flop – go back to the drawing board. That is why it is never too early to start testing and why testing should be ingrained into the design and development schedule