Run assumption tests as early as possible, ideally before you invest too much time and money into building your product. Assumption tests help you check if the key things you believe about your users, product, or market are actually true. The earlier you test, the sooner you can avoid mistakes and make better decisions. It’s a good idea to run assumption tests after you’ve identified a target opportunity and selected a few ideas to explore. This helps you figure out which idea has the best chance of success.

Also run tests after choosing a final solution, especially if there are still questions about how it will work or if there are risks you need to manage. Since assumption testing helps teams make smarter decisions, it should be done continuously throughout the discovery process as you explore what to build. Regular testing ensures you're always learning and improving your product ideas.