When you have a hypothesis and want to Validate your learning one could even offer a MVP or fake prototype and see how potential or actual customers interact with this.
Reference
Ries, Eric. The Lean Startup: How Today’s Entrepreneurs Use Continuous Innovation to Create Radically Successful Businesses. 1st ed, Crown Business, 2011.
Highlights or timestamps
Don’t use questionnaires or fictional customers though; instead, talk to real customers in a realistic environment. The most reliable way to find out whether people will buy your product is to offer it to them and see how they respond.
— ^94d35d from The Lean Startup