A test apparatus for an optical investigation system, with an imaging device and a light source for optical investigation of an object in remitted light and/or fluorescent light includes a housing with a hollow space and an aperture for inserting a distal end of the imaging device into the hollow space, a reference surface with predetermined optical properties in the hollow space, at least either for remission of illuminating light directed onto the reference surface or for emission of fluorescent light, and a positioning device to hold the imaging device of the distal end of the imaging device at a predetermined position in relation to the reference surface.