A testing device and a method for verifying the charge invoicing for a communications device according to time unit intervals is provided. A testing device, which can simulate at least one calling analog terminal and at least one called terminal, is connected to a network node that generates time pulses. At least one predetermined test communications connection is set up and terminated over at least the one network node. Further, the time interval between the beginning of the test communications connection and the generation of a first time pulse is determined and verified to ascertain whether the determined time interval is located within a first predetermined time domain. During the existing test communications connection, time unit intervals of successive time pulses are measured and compared with a predetermined time interval. A further method involving receipt of additional time pulse(s) after the termination of the test communications connection is also provided.