In recent years, agent-based systems have received considerable attention in both academics and industry. The agent-oriented paradigm can be considered a natural extension to the object-oriented (OO) paradigm. Agents differ from objects in many issues which require special modeling elements but have some similarities. Although there is a well-defined OO testing technique, agent-oriented development has neither a standard development process nor a standard testing technique. In this paper, we will give an introduction to most recent works presented in the area of testing distributed systems composed of complex autonomous entities (agents). We will provide pointers to work by large players in the field. We will explain why this kind of system must be handled differently than less complex systems.