The only test that matters is the market. The lean startup was the first book that sort of helped me understand that mindset, for any of its faults it is still

The only test that matters is the market. The lean startup was the first book that sort of helped me understand that mindset, for any of its faults it is still a classic for a reason and at least helps in shifting perspective from "create the perfect idea" to "find any problem that needs to be solved and begin iterating to a solution"