A display device and a testing method thereof are disclosed, in which a defect caused by an overflow of an organic film constituting an encapsulation film can be detected. The display device comprises a substrate including a display area where pixels are arranged, and a pad area including a plurality of pads formed outside the display area; an encapsulation film covering the display area, including at least one inorganic film and at least one organic film; a dam arranged between the display area and the pad area; and a conductive testing line arranged between the dam and the pad area and not electrically connected with another conductive line or electrode arranged on the substrate.