The development of a uniform and stable high velocity, thin liquid lithium film stripper is essential for the future Facility for Rare-Isotope Beams (FRIB). The formation of such a film has been demonstrated recently at ANL. The next step is to be able to measure the film thickness and verify its temporal and spatial stability under high power density ion beam irradiation. Intense beams of light ions generated by the FRIB prototype injector can be used to accomplish this task. The injector consists of an ECR ion source followed by a LEBT. Previously, a DC 3.3 mA/75 kV proton beam was delivered downstream of the first bending magnet. The proton beam power will be brought to the required level by adding a second accelerating tube. A low energy electron beam (LEEB) technique, based on the thickness-dependent scattering of electrons by the film, was proposed as a fast-response on-line film thickness diagnostic. A LEEB test bench has been designed and built to verify this technique off-line. The transmission of electrons through carbon foils of different thicknesses was measured and compared with the results of CASINO simulations. Comparing the experimental and numerical results we should be able to have a quantitative measurement of the film thickness.