An apparatus for testing an image sensor includes a load resistor, a first switch configured to be electrically connected to a first signal line of a device under test and a first end of the load resistor, a second switch configured to be electrically connected to a second signal line of the device under test and a second end of the load resistor, a first parametric measuring unit electrically connected to the first switch, and a second parametric measuring unit electrically connected to the second switch. At least one of the first parametric measuring unit and the second parametric unit is configured to correct an error of the load resistor during a testing operation of an output voltage of the device under test.