Phasor Measurement Units (PMUs) are getting increasingly popular. Major incidents in the near past, such as the big blackouts in 2003 in the northeast of the USA and in Italy, have raised the interest in all means that support the observation of the condition of the electrical power network, assessing system stability, and predicting problems. PMUs are perceived to be valuable tools for this. The paper gives a brief introduction to the principle of operation of PMUs and the metrics for assessing their performance. Some exemplary test cases are explained and possible test configurations to perform the test cases are discussed. The shown methods are not only suited for laboratory applications. The usage of a classical protection test set with versatile time synchronization interfaces (GPS, IRIG-B, PPS) brings PMU testing into the reach of protection engineers for applications in the field.