The Scope can be defined from the BRS, SRS, FRS or from functional points. It may be anything that is provided by the client. And regarding organizing we need to analyze the functionality to be covered and who will testing the modules and pros and cons of the application. Identify the number if test cases, resource allocation, what are the risks that we need mitigate all these come into picture. Once this is done it is very easy to execute based on the plan what we have chalked out.