On theory of fuzzy tests

In diagnosis problem of the paper the distinguishability of objects in indistinguishable, weakly distinguishable, distinguishable, well-distinguishable values of features stays withing an interval of [0, 1] rather than is a binary (0, 1) (distinguishable, indistinguishable) value. Theory of fuzzy sets helps introduce concepts of fuzzy tests and cul-de-sac fuzzy tests. Usual test for binary tables are shown to be a particular case of fuzzy sets. A method of designing cul-de-sac fuzzy sets with the aid of fuzzy logic is described.