For test renders it is sometime required to render a specific area in camera view rather than to render the whole view and at end you feel something is wrong.
To render selected area in blender press Shift-B in camera view and then with marquee selection select the area you want to have test render. If you render now it will only render the area you selected.
To render the full camera view again press shift-B and take selection outside the camera view.
Have a good day cheers🙂