E. Rossoni proposes two possible origins for this surname. On the one hand, it could derive from the Latin praenomen of Greek origin Testorius, documented in the Genealogiae deorum gentilium of Boccaccio. On the other, it could come from a nickname linked to the trade of testore ("weaver"), a term cited in a testament of 1611. Rossoni records the transformation into a surname in Garlate during the 17th century, and notes that Testori is typical of western Lombardy, while the variant Testorio is extremely rare.

R. Brondolo agrees on the occupational base, but specifies the phonetic process: the surname would derive from tessitore ("weaver") through syncope, that is, through the suppression of internal syllables that would have given rise to the reduced form testore and, later, to Testori.