This paper focuses on the trade-off algorithm, which is a core part of the allocation for testability process of a High-Level Synthesis for Testability system. The allocation for testability is mainly defined as the search for best cost/quality trade-offs between the designer requirements and testability means that can be proposed by the system, considering the available functional units in a library and the possibility to generate additional testability structures. The paper first presents the defined methodology and the considered criteria, and then gives example results.