A display device includes a display area, a test pad, a plurality of first test transistors, and at least one outline. The display area includes pixels coupled to data lines and scan lines. The test pad receives a test signal. The first test transistors are coupled between the data lines of the display area and the test pad. The at least one outline is coupled between one of the first test transistors and the test pad. The at least one outline is located in a non-display area outside the display area.