Abstract: A test system for a stored program controlled time-division switching network subdivided into subsystems. The test system includes circuits for selecting, injecting and retrieving data samples and testing for the correct setting of switchpaths through the switching network. A stored program control unit receives test instructions and transmits in response thereto reporting messages including retrieved data samples. A selection control circuit interconnects the subsystems to which a test instruction relates. The subsystems are provided with an interchange circuit for receiving and storing samples, a sample injection and retrieval circuit, and a circuit for synchronizing the receiving and storing circuit with time slot information identifying a sample which has been received and the sending circuit with the time slot into which a sample is injected.