The exact null distribution of the generalized Hollander-Proschan type   test for NBUE alternatives
  In this note we derive the exact null distribution for the test statistic proposed by Anis and Mitra (2011) for testing exponentiality against NBUE alternatives. As a special case, we obtain the exact null distribution for the test statistic proposed by Hollander and Proschan (1975). Selected critical values for different size are tabulated for these two statistics. Some remarks concerning the benefits of using the exact distribution are made. 
M.Z. Anis and Kinjal Basu
math.ST stat.TH