Is this book for Agile or waterfall projects? Both!
This book does not discuss different development models such as Agile or waterfall. Whichever you are using, you will need to design a comprehensive test plan to exercise new features and discover their defects.
However, there will be significant timing differences depending on the method you’re using. Waterfall projects may extend over many months, with weeks allocated to the different areas of testing described here. In contrast, Agile projects rapidly cycle through the different types of testing, doing a little of each in cycle after cycle.
Despite their differences, both project types, and the many real-world hybrids used in practice, require a thorough test plan covering the many different aspects of system behavior. Whatever project type you work on, this book can help you write better test plans.