The Collaborative International Dictionary of English v.0.48:

Testiness \Tes"ti*ness\, n.
   The quality or state of being testy; fretfulness; petulance.
   [1913 Webster]

         Testiness is a disposition or aptness to be angry.
                                                  --Locke.
   [1913 Webster]

WordNet (r) 3.0 (2006):

testiness
    n 1: feeling easily irritated [syn: testiness, touchiness,
         tetchiness]