Researchers across the globe are carrying out numerous experiments related to cybersecurity, such as botnet dispersion, intrusion detection systems powered by machine learning, and others, to explore these topics in many different contexts and environmental settings. One current research topic is the behavior of Internet of Things (IoT) devices, as they increasingly become a common feature of homes, offices, and companies.. Network testing environments which are designated as testbeds, are boosting the effectiveness of network research. However, exploratory studies in IoT cybersecurity may include a wide range of requirements. This article seeks to carry out a survey of IoT cybersecurity testbeds. A critical systematic literature review was conducted to select relevant articles, by applying a novel taxonomy to classify the testbeds. The surveyed testbeds are classified in terms of their primary target domain and other features such as fidelity, heterogeneity, scalability, security, reproducibility, flexibility, and measurability. Furthermore, we have compared the testbeds with regard to each feature. Thus, the main contribution made by this study lies in a) the insights it provides into the state-of-the-art in IoT cybersecurity testbeds, and b) the emphasis laid on the main benefits and limitations that were found in the surveyed testbeds.