A cable tester is a device used to test the strength and connectivity of a particular type of cable or other wired assemblies. There are many different types of cable testers. Each of them can test a specific type of cable or wire (some may be able to test different types of cables or wires). A cable tester can test whether a cable or wire is set up properly, connected correctly, and the communication strength between the source and destination. The picture is an example of a cable tester from TRENDnet.
For computers, one of the most common types of cable testers used is for testing Cat 5, Cat 5e, and Cat 6 network cables. Because so many different types of data are transmitted over a network cable, a proper connection needs to be established between the computer and server. Also, make sure the signal strength is adequate for transmitting data and that there is no outside interference. A cable tester can test for these factors and verify the network cables connections are correct and work for the intended purpose.