  The Ultra-Fast Flash Observatory pathfinder (UFFO-p) is a new space mission
dedicated to detect Gamma-Ray Bursts (GRBs) and rapidly follow their afterglows
in order to provide early optical/ultraviolet measurements. A GRB location is
determined in a few seconds by the UFFO Burst Alert & Trigger telescope (UBAT)
employing the coded mask imaging technique and the detector combination of
Yttrium Oxyorthosilicate (YSO) scintillating crystals and multi-anode
photomultiplier tubes. The results of the laboratory tests of UBAT's
functionality and performance are described in this article. The detector
setting, the pixel-to-pixel response to X-rays of different energies, the
imaging capability for <50 keV X-rays, the localization accuracy measurements,
and the combined test with the Block for X-ray and Gamma-Radiation Detection
(BDRG) scintillator detector to check the efficiency of UBAT are all described.
The UBAT instrument has been assembled and integrated with other equipment on
UFFO-p and should be launched on board the Lomonosov satellite in late-2015.
