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. 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.