An early use of the term "testimator" way made by Brewster & Zidek (1974).2
Adke, S.R., Waikar, V.B. & Schurmann, F.J. (1987). "A two stage shrinkage testimator for the mean of an exponential distribution". Communications in Statistics - Theory and Methods, 16 (6), 1821-1834. Retrieved April 16, 2009, from http://www.informaworld.com/10.1080/03610928708829474 (restricted access) /wiki/Communications_in_Statistics#Communications_in_Statistics_–_Simulation_and_Computation ↩
Brewster, J.F., Zidek, J.V.(1974) "Improving on Equivariant Estimators". Annals of Statistics, 2 (1), 21–38 /wiki/Annals_of_Statistics ↩