Test system, method of testing display cell using the same, and display device

A method of testing a display cell, the method comprising:

• outputting, by a test member, a first test control signal in a data test mode;
• outputting, by the test member, a second test control signal in a sensing test mode;
• outputting, by an optical sensor, a test sensing signal to a readout line connected to the optical sensor, the test sensing signal being generated according to external light;
• connecting a test signal line of a signal selection unit to the readout line in response to the second test control signal;
• and
• connecting a data line connected to a pixel to the test signal line in response to the first test control signal,
• wherein a first switching transistor is configured to be turned on in response to the first test control signal to connect the test signal line to the data line, the first switching transistor comprises a source electrode and a drain electrode neither of which is connected to the readout line, a second switching transistor is configured to be turned on in response to the second test control signal to connect the test signal line to the readout line, and the second switching transistor comprises a source electrode and a drain electrode neither of which is connected to the data line, and
• wherein the readout line is separated from the data line;
• receiving, by the test member, the test sensing signal from the optical sensor in the sensing test mode and test whether or not the optical sensor normally operates.

A display device comprising:

• a substrate;
• a pixel and an optical sensor disposed on the substrate;
• a data line connected to the pixel;
• a readout line connected to the optical sensor;
• a first floating line and a second floating line exposed through one side surface of the substrate;
• a first switching transistor connected between the first floating line and the data line;
• and
• a second switching transistor connected between the second floating line and the readout line.