Interoperability is a challenge for the realisation of smart grids. In this work, we first present an interoperability testing methodology, which is substantial to perform interoperability tests for the smart grid. To show its applicability and facilitate its comprehension, we present an example by applying it on a Demand Side Management (DSM) use case. The DSM use case is chosen because it is a major topic for modern grids and it involves the participation of many actors. The tutorial exemplifies the interactions among those actors. The Smart Grid Architecture Model SGAM framework is used, where the mapping of the use case is presented along with the Message Sequence Chart (MSC). Then we describe the profiling of the equipment, relevant technical information and standards, which form the basis for the design and execution of the interoperability tests. We focus on the technical part of the interoperability testing; therefore, attention is focused on the information and communication layer. We present how the interoperability tests should take place and we analytically show the respective Test Cases (TC). The verdict of the test should be either PASS or FAIL. The paper shows how to successfully use the methodology for interoperability testing on a specific use case, whereas its applicability can be extended to any smart grid interoperability use case.