In this paper we study how to verify that a pure Prolog program has solutions for a given query. The detailed analysis of the failure/ success behaviour of a program is necessary when dealing with transformation and verification of pure Prolog programs. In a previous work [10] we defined the class of noFD programs and queries which are characterized statically. We proved that a noFD query cannot have finitely failing derivations in a noFD program. Now, by introducing the concept of a set of exhaustive tests, we define the larger class of successful predicates. We prove that a noFD terminating query for successful predicates have at least one successful derivation. Moreover we propose some techniques based on program transformations for simplifying the verification of the successful condition.