Testing virtualised network functions

According to a first aspect, there is provided a method of testing a plurality of virtual network functions (VNFs) during commissioning of the plurality of VNFs in a virtualized environment in a customer network, the method comprising: at a VNF testing component configured to have access to the virtualized environment of the customer network, performing interoperability testing between a first VNF component instantiation (VNFCI) within a first VNF of the plurality of VNFs and a second VNFCI within a second VNF of the plurality of VNFs, the second VNF being different from the first VNF, the first VNF and the second VNF comprising a subset of VNFs within the plurality of VNFs, wherein performing the interoperability testing comprises: instructing the first VNFCI to interoperate directly with the second VNFCI in a predetermined manner; and determining whether the second VNFCI reacts to the instructed direct interoperation in an expected manner.