  Considerable progress has been made over the last decade in understanding the
phenomenological properties of the cuprate high-T$_{c}$ superconductors and in
producing well characterized high quality materials. Nevertheless, the pairing
mechanism itself remains controversial. We establish a criterion to test
theories for layered superconductors relying on a substantial interlayer
contribution. The criterion is based on the ratio of the interlayer
contribution to the total superfluid density, which is traced back to the
inverse squared effective mass anisotropy. The anisotropy can be measured
rather accurately by various experimental techniques. It turns out that models
relying on interlayer pairing cannot be considered as serious candidates for
the mechanism of superconductivity in cuprate superconductors.
