1. An image forming apparatus comprising: an image bearing member configured to bear an image with a toner; a transfer unit configured to transfer the image from said image bearing member onto a recording material; a conveying unit configured to convey the recording material having the image on a first side thereof to transfer the image onto a second side of the recording material; a control unit configured to control an operation for forming a test image in an interval region between a first image, formed on said image bearing member, and a second image formed subsequently to the first image on said image bearing member; wherein said control unit is configured to permit formation of the test image in the image interval region when the second image is an image to be transferred onto a first side of the recording material and configured to prevent formation of the test image in the image interval region when the second image is an image to be transferred onto a second side of the recording material.