A display device includes a substrate including a display area and a test area adjacent to the display area, a lower electrode disposed in the display area on the substrate, a common layer disposed on the lower electrode, an upper electrode disposed on the common layer; and a test element group. The test element group includes a plurality of electrode patterns disposed in a same layer as the lower electrode and in the test area on the substrate, a test common layer disposed in a same layer as the common layer and on the electrode patterns, where a plurality of openings is defined through the test common layer to expose a part of each of the electrode patterns, and an electrode layer disposed in a same layer as the upper electrode, on the test common layer, and in contact with the electrode patterns through the openings.