A method for testing the deposition and/or the removal of a material within a recess on the surface of a sample. An excitation beam is directed onto a region of the sample in a vicinity of the recess, and an intensity of X-ray fluorescence, emitted from the region in a spectral range in which the material is known to fluoresce, is measured. A quantity of the material that is deposited within the recess is determined responsive to the measured intensity.