Geometry of the analytical test cases. The z-axis is oriented toward the reader and −y toward the observer. TC 1: a central point source illuminates thin slabs of electrons that are slanted 45° toward the observer. For the other test cases, the central point source is replaced by a small cloud of electrons. TC 2: the cloud is illuminated by a collimated beam, which is located in the xy plane. TC 3-TC 4: the illuminating source is located below the xy plane.