Agile software development in general and Extreme Programming (XP) in particular, promote radical changes in how software development organizations traditionally work. We present and analyze new data from a real, large-scale agile project to develop a business-critical enterprise information system for the Israeli Air Force (IAF). Our results offer new evidence that agile testing practices actually work, dramatically improving development quality and productivity. We describe the organization's successful practices and guidelines in four key areas: test design and activity execution, working with professional testers, planning, and defect management