This contribution provides an overview on the common on-site test methods to ensure the safe and reliable operation of circuit breakers used in high and medium-voltage power systems. Failures on circuit breakers can generally be ascribed to defects in one or more of the three main components: The operating mechanism incl. mechanical linkage, the electrical control circuits and the components at system voltage. Therefore, detecting wear and tear processes in these components of the circuit breaker during scheduled maintenance procedures reduces the risk of failures during operation. The standard on-site testing practices include timing, travel and coil current signature measurements to assess the integrity of the kinematic chain and control circuits. In addition, micro-ohm measurements are performed on the breaker’s main contacts. This paper discusses the advantages and disadvantages of these standard practices and how to interpret measurement results. Furthermore advanced testing methods are introduced that can easily be applied using the latest testing technology.