The fewer requirements you probe in depth, the more risk you incur. However, you're taking dangerous chances if you don't learn enough about the product's requirements to decide what to test and at what depth. Customer requirements are the design decisions about your customer's problem. Use those design decisions to solve that problem with your product. Functions Functions are actions the system performs which appear as verbs in statements.
Many people have different pieces of the picture.
Programmers have been programming their bits. Marketers have been setting customers' expectations. Architects, managers, designers, and others have been discussing requirements in a variety of forums. Most often, their discussions focus on functions, rather than attributes. Lots of assumptions have been made.