Current in-vehicle electronics are based on networked modules. Knowing this and taking into account the rapidly increasing number of network nodes in cars, the proper functionality and interoperability of network interfaces produced by various manufacturers is an important pre-requisite in order to obtain a good quality system operation. One way to ensure good interoperability of network interfaces is to apply conformance tests.The following paper therefore outlines the specification of such conformance tests, as they are defined by ISO. Along with the specification of standard conformance tests a set of test extension is proposed checking the proper functionality of a network interface according to its register interface to the processor and its proper behavior in (random) stress situations - referred to as random or robustness tests. Finally an implementation of a tester performing the conformance tests is introduced. All conformance tests are explained for checking CAN communication protocol, but they can be rather easily mapped to other protocols such as J1850. The paper is rounded out by indicating that these communication protocol tests are to be proliferated towards “higher system level” tests such as operating system tests and incoming inspections at customers' sites, etc.