A testing device includes a positioning assembly and a testing assembly. The positioning assembly positions a workpiece. The testing assembly tests the workpiece. The positioning assembly includes a mounting seat defining a receiving slot for receiving and positioning the workpiece. The mounting seat includes a first positioning surface and a second positioning surface. The positioning assembly includes a side pusher configured to move toward the receiving slot. The side pusher includes a first pushing surface and a second pushing surface. When the side pusher is driven to move toward the receiving slot, the first pushing surface and the second pushing surface push two surfaces of the workpiece to make opposite two surfaces of the workpiece come in contact with the first positioning surface and the second positioning surface to position the workpiece in the receiving slot.