A display device and a method of testing the display device. The display device includes a substrate including both a display region on which pixel cells are located and a peripheral region; test pads, main pins connected to the pixel cells, and dummy pins that are respectively connected to the test pads, the test pads, the main pins, and the dummy pins being on the peripheral region of the substrate, and visual test lines on the peripheral region of the substrate. The visual test lines include a first portion connected to the main pins and a second portion connected to the test pads, and the first and second portions are disconnected from each other.