tester (n.1)
"one who tests, puts to trial, or assays," 1660s, agent noun from test (v.). Earlier "a crucible" for trying metals by heating them (mid-15c.).
tester (n.2)
"canopy over a four-post bed," mid-14c., from Medieval Latin testerium, from testera "head-stall" of the bridle of a horse, extended use and form of Late Latin testa "skull," in Vulgar Latin "head" (see tete). From Medieval Latin testa as "head" also come tester in obsolete senses of "piece of armor for the head" (late 14c., via Old French testiere) and "coin of Henry VIII" (1546), the first English coin to bear a true portrait.