An apparatus for the testing of downhole a injection assembly prior to installation of the injection assembly in the completion string. The apparatus is comprised an injection tubing, an injection sub, an injection valve, an injection sub test block, a pressure foot, a pressure foot test block, and means for introducing pressure at a desired level. The injection sub test block, pressure foot, pressure foot test block are interchangeably engageable with the injection sub for testing in a sequence to allow the pre-testing of the connections of components of the injection assembly at the surface of the well.