  Triple-GEM detectors for the GE2/1 and ME0 stations of the endcap muon system
for the Phase-2 upgrade of the CMS Experiment have been operated in a test beam
to measure their efficiency and spatial resolution, together with a high
spatial resolution triple- GEM tracker. A production module of GE2/1 detectors
and a prototype ME0 detector show excellent local efficiency. A prototype
detector with GEM foils employing random hole sectorization showed significant
reduction of dead areas. The spatial resolution of the tracker has been
measured and found close to the expected value of 75 {\mu}m.
