A testing arrangement for testing the electrical circuits of a terminal block assembly, comprising a generally rectangular testing unit housing formed of insulating material and containing a chamber, at least one connection device mounted in chamber and having an elongated connector body formed of insulating material and including center and end portions. An integral measuring tab portion extends downwardly from the body center portion for insertion into a testing opening contained in the terminal block assembly, and a pair of coplanar measurement portions extend upwardly from the connector body ends and terminating at different elevations, thereby to afford a compact testing arrangement. Two electrical circuit connecting portions are mounted on the connector body, each including an input conductive contact plate mounted on one side of said measuring tab portion, and an output contact mounted within one of said measurement portions for connection with one end of a testing component.