The best user research and usability testing is early, often, and continuous – as much as possible.

The more the team can observe user responses, frustrations, and successes in a real context and in real use, the more the design solutions are validated and conform to the business goals and user goals early in the development which saves money, time, and provides greater confidence for success. Any chance for paper-based, “guerrilla” testing all he way to full-blown recorded studies are well spent.