Some people say they “don’t have enough requirements to start testing,” or that the requirements are unclear or incomplete or contradictory or out of date.
First, those people usually mean requirements documents; don’t confuse that with requirements, which may be explicit or tacit. There are plenty of sources of requirements-related information, and it’s a tester’s job to discover them and make inferences about them.
Second, insufficient clarity about requirements is both a test result and a project risk, and awareness of them may be crucially important project information. (If the testers aren’t clear on the requirements, are the programmers? And if they’re not, how is it that they’re building the product?)
Finally, if there is uncertainty about requirements, one great way around that problem is to start testing and reporting on what you find. “Insufficient requirements” may be a problem for testing—but it’s also precisely a problem that testing can help to solve.