A display device and a testing method thereof are disclosed, in which a defect caused by an overflow of an organic film (292) constituting an encapsulation film (290) can be detected. The display device comprises a substrate (111) including a display area (DA) where pixels are arranged, and a pad area (PA) including a plurality of pads formed outside the display area; an encapsulation film (290) covering the display area, including at least one inorganic film (291) and at least one organic film (292); a dam (120) arranged between the display area and the pad area; and a conductive testing line (130) arranged between the dam (120) and the pad area (PA) and not electrically connected with another conductive line or electrode arranged on the substrate (111).