  To fulfill the requirements for testing the photomultiplier tubes (PMTs) of
the electromagnetic detec- tor at the Large High Altitude Air Shower
Observatory (LHAASO), a multi-functional PMT test bench with a two dimensional
scanning system has been developed. With this 2D scanning system, 16 PMTs can
be scanned simultaneously for characteristics tests, including uniformity,
cathode transit time difference, single photo-electron spectrum, gain vs. high
voltage, linear behavior and dark noise. The programmable hardware and
intelligent software of the test bench make it convenient to use and provide
reliable results. The test methods are described in detail and primary results
are presented.
