Usability testing in product design serves the purpose of evaluating a product’s user-friendliness and effectiveness by observing real users interacting with it. This process identifies any pain points, confusion, or challenges that users encounter, providing insights into both functional and design aspects. By gathering qualitative and quantitative feedback, designers can make informed adjustments to improve the product's interface, functionality, and overall user experience. Ultimately, usability testing helps ensure that the product meets the needs of its intended audience.