A device for testing a data carrying service operating over a telecommunications line includes a plurality of test circuits. Each test circuit is arranged to determine and test one or more characteristics of a data carrying service and a termination of the telecommunications line is emulated. The operation of each of the plurality of test circuits is controlled, and the telecommunications lines is connected to one or more of the plurality of test circuits. The data carrying service remains connected via a connection during all of the testing operations provided by one or more of the test circuits which enables the device to automatically determine the identity of the data carrying service. The test circuits may be arranged to enable emulation of a termination to be interconnected so as to enable the device to provide a passive link in the data carrying service and/or provide throughput testing of the telecommunications line.