1. An image forming apparatus comprising: at least one image forming unit comprising: an image bearing member configured to bear an electrostatic latent image thereon; and a developing device configured to develop the electrostatic latent image with a developer comprising a toner to form a toner image on the image bearing member; a transfer device configured to transfer the toner image on the image bearing member to a receiving material optionally via an intermediate transfer medium; an image pattern measuring device configured to evaluate at least one formal property of a test toner image formed on the image bearing member or the intermediate transfer medium; an image quality predicting device configured to predict image qualities of the toner image to be formed on the receiving material on the basis of the evaluation data of the at least one formal property of the test image; and an image forming condition adjusting device configured to adjust image forming conditions on the basis of the image quality prediction data.