A testing method includes: providing a camera under test and a planar light source having a first mark, wherein the camera includes a voice coil motor (VCM) and a lens module is fixed on the VCM by glue, the VCM moves the lens module, the VCM includes an elastic tab for limiting and restoring the movement of the lens module; taking an image of a light source using the camera during the movement of the VCM; displaying the image having the first mark; determining if the first mark tilts using a detector; displaying a first message indicating that the tab is not stuck by glue when the detector determines the first mark does not tilt; and displaying a second message indicating that the tab is stuck by glue when the detector determines the first mark tilts.