This paper presents a combination of verification and conformance testing techniques for the formal validation of reactive systems. A formal specification of a system - an input-output automaton with variables that may range over infinite domains - is assumed. Additionally, a set of safety properties for the specification are given under the form of observers described in the same formalism. Then, each property is verified on the specification using automatic techniques (e.g., abstract interpretation) that are sound but not necessarily complete for the class of safety properties considered here. Next, for each property, a test case is automatically generated from the specification and the property and is executed on a black-box implementation of the system. If the verification step was successful, that is, it has established that the specification satisfies the property, then the test execution may detect the violation of the property by the implementation and the violation of the standard ioco conformance relation[18] between implementation and specification. On the other hand, if the verification step did not conclude (i.e., it did not allow to prove or to disprove the property), then the test execution may additionally detect a violation of the property by the specification. The informations about the relative (in)consistencies between specification, implementation, and properties are reported to the user as test verdicts. The approach is illustrated on the BRP protocol [9].