The present document describes an assembly for connecting a test unit to a wiring harness or equipment to be tested, and a method for testing using the assembly. The assembly may comprise a test box unit, a generic mate-in interface, and at least one specific mate-in interface. The generic mate-in interface is for connection to the test box unit on one end, and to the at least one specific mate-in interfaces at the other end. The mate-in interfaces are for testing different existing wiring harnesses or equipment. Each one of the generic and specific mate-in interfaces has a specific ID comprised in an ID support on the electrical path of the generic mate-in interface and the specific mate-in interface, for example, on any one of the end connectors of the interfaces or on their wiring. Information relating to the IDs of the connectors and the contact configuration of each mate-in interface is stored in a database of the test unit for identifying the appropriate test contacts that should be used for testing.