1. An image output apparatus comprising: an image forming unit that forms an image on a recording medium; a test-threshold acquiring unit that acquires a test threshold that is a pass-fail criterion for an image test and compares test image data, the test image data being generated by an image reading apparatus by using the image formed on the recording medium and being used as a test object for the image test, with reference image data, the reference image data being used as a test reference for the image test, to determine whether the test image data passes or fails the image test based on the acquired test threshold; a changing unit that changes a density detection mode of at least one of the image forming unit and the image reading apparatus on the basis of the test threshold; a density correcting unit that corrects density used in an image forming process performed by the image forming unit, on the basis of a result of density detection performed after the density detection mode is changed; and a reference-image-data acquiring unit that acquires the reference image data, wherein the image forming unit forms an image of the reference image data on a recording medium at the corrected density.