Prototyping is a crucial step in the UX design process as it enables designers to create a working model of the product. It allows for early validation of UX designer's job, ideas, and quick identification of potential issues. User testing, on the other hand, provides from real users, ensuring that the final product aligns with user needs and expectations by also using UX research. These two stages help in preventing costly rework and creating a more successful final product at the end of the UX process.