“We define an agile tester this way: a professional tester who embraces change, collaborates well with both technical and business people, and understands the concept of using tests to document requirements and drive development. Agile testers tend to have good technical skills, know how to collaborate with others to automate tests, and are also experienced exploratory testers. They’re willing to learn what customers do so that they can better understand the customers’ software requirements.” Source: “Agile Testing”, Lisa Crispin and Janet Gregory, Addison-Wesley, 2009
Agile testing tutorials and how to content : Test-Driven Development (TDD), Behavior-Driven Development (BDD) and other agile approaches for software testing.
This article “XP Testing Without XP: Taking Advantage of Agile Testing Practices” describes how to use techniques from extreme programming for teams that have not implemented XP