Practitioners report that experience plays an important role in effective software testing. We investigate the role of experience in a multiple case study about three successful projects conducted at Siemens Austria and document the state of practice in testing software systems. The studied projects were employed from the domains telecommunications, insurance and banking, as well as safety-critical railway systems. The study shows that test design is to a considerable extent based on experience in all three projects and that experience-based testing is an important supplementary approach to requirements-based testing. The study further analyzes the different sources of experience, the perceived value of experience for testing, and the measures taken to manage and evolve this experience.