The emergence of small, inexpensive, network-capable sensing devices led to a great deal of research on the design and implementation of sensor networks. A critical step in taking protocols from theory to actual deployment is comprehensive testing on physical sensor networks. Sensor network testbeds provide one way to facilitate such testing without requiring the deployment of a specialized sensor network for each protocol. However, for such testbeds to be useful, they must not overwhelm researchers with maintenance tasks and high learning curves. Previous work in testbed design has primarily focused on creating interfaces to maximize their usage by convenient scheduling of jobs and output access. In this work, we present two contributions to sensor network testbed design. The first is a unique management tool that allows users to program, interact with, and receive data from nodes in the network, filling a gap in current testbed management solutions. The second is the design, deployment, and analysis of the SignetLab testbed. The analysis of the testbed and its results provide quantitative measurements of the impact of physical deployment on signal propagation characteristics. Additionally, we present two case studies where researchers have used the testbed and discuss the user experiences and lessons learned.