What is the point when testing should begin for an application which is about to be developed?

It’s a common misconception that testing actually begins when the
development of the module is completed. It’s a misunderstood concept. If we go by  the SDLC phases, testing starts at the time when the requirement analysis is  going on. Verifying requirement documents, design documents, creating test  approach, test scenarios and test cases based on available documents or  discussion is also part of testing and this is also known as verification phase.