Models assuming minimal repair specify that on repair, a failed system is returned to the working state, while the effective age of the system is held constant; that is, the distribution of the time until the next failure of the repaired system is the same as for a system of the same age that has not yet failed. These models are common in the literature of operations research and reliability, and many probabilistic results as well as inferential procedures depend on the minimal repair assumption. We propose two nonparametric tests of the assumption that imperfectly repaired systems are minimally repaired in some models. The large sample theory for these tests is derived from the asymptotic joint distribution of a survival function estimator and the ordinary empirical survival function based on the initial failure times of new or perfectly repaired systems. Simulation results are also provided for the null hypothesis case and under other alternatives.