  A Cosmic Muon Veto Detector (CMVD) is being built around the mini-Iron
Calorimeter (mini-ICAL) detector at the transit campus of the India based
Neutrino Observatory, Madurai. The CMV detector will be made using extruded
plastic scintillators with embedded wavelength shifting (WLS) fibres which
propagate re-emitted photons of longer wavelengths to silicon photo-multipliers
(SiPMs). The SiPMs detect these scintillation photons, producing electronic
signals. The design goal for the cosmic muon veto efficiency of the CMV is
$>$99.99\% and fake veto rate less than 10$^{-5}$. A testing system was
developed, using an LED driver, to measure the noise rate and gain of each
SiPM, and thus determine its overvoltage ($V_{ov}$). This paper describes the
test results and the analysed characteristics of about 3.5k SiPMs.
