Abstract: A testing and switching (tester) system is disclosed for information transmission and communications networks and systems and the like. According to a preferred embodiment, a data transmission network is advantageously of the type in which remotely located users or customers are afforded time-shared access to a centrally located computer. The data transmission network includes remotely located switching stations which are linked to the central computer over data transmission lines which include selectively actuated normal and fallback local loops. The network users gain access to the centrally located computer over selectively actuated local lines to the remotely located switching stations. The tester system comprises switching and testing apparatus which includes a programmable tester computer located at the remotely located stations and preferably at the centrally located computer site also.