In this paper, we propose the use of accessibility measures in some testing strategies to specify testing objectives based on a functional model. The functional model, which is founded on the information transfer within software, was used with success to analyze testability for data-flow software. The testing strategies based on this model allow specification of testing objectives in relation to faults diagnostic, i.e. they allow not only faults to be detected but also to be located in the software. The approach is applied on a data-flow design provided by THALES Avionics to specify testing objectives.