The invention discloses a testing device and a detection method. The testing device is used to provide a testing signal for a to-be-tested module which has a first input port with the first polarity and a second input port with the second polarity. The testing device comprises a drive module for generating a first test signal having a first polarity and a second test signal having a second polarity, a control module for generating a control signal based on the first test signal, and a relay for providing a test signal for the backlight module to match the polarity of the first input port and the second input port of the backlight module. The testing device and the detection method disclosed in the invention can realize the automatic matching of the polarity of the testing device and the to-be-tested module, the test operation can be completed normally regardless of whether the polarity of the connection terminals of the testing devices and the to-be-tested module is matched or not, and the problem that the testing device cannot be used normally due to wrong connection of the operator, and the working efficiency is caused to be reduced in the prior art is solved.