Applications of the Internet of Things (IoT) require validation considering many types of environments before their actual implementation. Generally, the validation of these systems may be conducted by software through the use of emulators and simulators. However, the validation by software has limitations that can prevent a realistic approximation of the system behavior in real environments. For this reason, the scientific community has dedicated a great deal of effort to develop experimental testbeds. In light of this, we present a review of the state-of-the-art related to the testbeds for wireless sensor networks and IoT applications. In addition, we carried out a comparative analysis considering the technical specifications of the selected testbeds and highlighted their capabilities. Finally, we conclude with a discussion of the advantages and limitations of the testbeds with regard to the key requirements needed for IoT experimentation.