The Collaborative International Dictionary of English v.0.48:

Testy \Tes"ty\, a. [Compar. Testier; superl. Testiest.] [OF.
   testu obstinate, headstrong, F. t[^e]tu, fr. OF. teste the
   head, F. t[^e]te. See Test a cupel.]
   Fretful; peevish; petulant; easily irritated.
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         Must I observe you? must I stand and crouch
         Under your testy humor?                  --Shak.
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         I was displeased with myself; I was testy. --Latimer.
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