On the Generation of Test Data for Prolog by Partial Evaluation

In recent work, we have proposed an approach to Test Data Generation (TDG) of imperative bytecode by partial evaluation (PE) of CLP which consists in two phases: (1) the bytecode program is first transformed into an equivalent CLP program by means of interpretive compilation by PE, (2) a second PE is performed in order to supervise the generation of test-cases by execution of the CLP decompiled program. The main advantages of TDG by PE include flexibility to handle new coverage criteria, the possibility to obtain test-case generators and its simplicity to be implemented. The approach in principle can be directly applied for TDG of any imperative language. However, when one tries to apply it to a declarative language like Prolog, we have found as a main difficulty the generation of test-cases which cover the more complex control flow of Prolog. Essentially, the problem is that an intrinsic feature of PE is that it only computes non-failing derivations while in TDG for Prolog it is essential to generate test-cases associated to failing computations. Basically, we propose to transform the original Prolog program into an equivalent Prolog program with explicit failure by partially evaluating a Prolog interpreter which captures failing derivations w.r.t. the input program. Another issue that we discuss in the paper is that, while in the case of bytecode the underlying constraint domain only manipulates integers, in Prolog it should properly handle the symbolic data manipulated by the program. The resulting scheme is of interest for bringing the advantages which are inherent in TDG by PE to the field of logic programming.