Robotic systems are increasingly a part of everyday life. Characteristics of robotic systems such as interaction with the physical world, and integration of hardware and software components, differentiate robotic systems from conventional software systems. Although numerous studies have investigated the challenges of software testing in practice, no such study has focused on testing of robotic systems. In this paper, we conduct a qualitative study to better understand the testing practices used by the robotics community, and identify the challenges faced by practitioners when testing their systems. We identify a total of 12 testing practices and 9 testing challenges from our participants' responses. We group these challenges into 3 major themes: Real-world complexities, Community and standards, and Component integration. We believe that further research on addressing challenges described with these three major themes can result in higher adoption of robotics testing practices, more testing automation, and higher-quality robotic systems.