The paper is concerned with testing nonparametric hypotheses about the underlying support G of independent and identically distributed observations. It is assumed that G belongs to a class G of compact sets with smooth upper surface called boundary fragments. It is required to distinguish the simple null hypothesis speci®ed by a known set G 0 in G against nonparametric alternatives that G belongs to a class obtained by removing a certain neighbourhood of G 0 in G . Using the asymptotic minimax approach, the problem is to determine the order of the smallest distance between the null hypothesis H 0 and the alternatives for which one is able to test the null hypothesis against the alternatives with a given summarized error.