TDR
A cable tester that uses time domain reflectometry is called a TDR (time domain reflectometer).
TDRs can detect the overall length of the cable, or detect the distance to a cable break or open point. This is because the signal is reflected anytime that the wiring is open.
Good TDRs show various levels of signal change along the way.
These measurements can tell you how efficient the wiring at a connector or patch panel.
If the measurement is made through a wall jack or patch panel, tiny spikes may appear at the connector showing the signal transition. A large spike could indicate a wiring problem or faulty connection.