Agile software development implies major changes in the way you test software, from strategic project planning to day-to-day activities. While previous publications focus on programmer-oriented practices, such as test-first programming, they've neglected many issues related to large-scale projects and to an organization's initial transition to agile methods. This article attempts to close this gap, reporting on the Israeli Air Force's Extreme Programming experiences in a large-scale, enterprise-critical software project. Along with qualitative and quantitative data that validates agile testing practices, the article presents guidelines for test design and execution, working with professional testers, planning the quality process, and defect management.This article is part of a special issue on Software Testing.