The emergence of Internet of Things (IoT) technology is expected to offer new promising solutions in various domains and, consequently, impact many aspects of everyday life. However, the development and testing of software applications and services for IoT systems encompasses several challenges that existing solutions have not yet properly addressed. Particularly, the difficulty to test IoT systems - due to their heterogeneous and distributed nature -, and the importance of testing in the development process give rise to the need for an efficient way to implement automated testing in IoT. Although there are already several tools that can be used in the testing of IoT systems, a number of issues can be pointed out, such as focusing on a specific platform, language, or standard, limiting the possibility of improvement or extension, and not providing out-of-the-box functionalities. This paper describes Izinto, a pattern-based test automation framework for integration testing of IoT systems. The framework implements in a generic way a set of test patterns specific to the IoT domain which can be easily instantiated for concrete IoT scenarios. It was validated in a number of test cases, within a concrete application scenario in the domain of Ambient Assisted Living (AAL).