Lecture Notes in Computer Science 3472

14 Tools for Test Case Generation 405
corresponding values are chosen randomly again to obtain a complete test sequence.
The test sequence generation is implemented in Prolog and based on the
ECLiPSE package [ECLb].
Domain Splitting
The basic testing method described above allows to generate a single test sequence.
GATeL offers the possibility of “domain splitting”, i.e., to replace the
domain (described by the current constraint set) with two ore more sub-domains
(again described by constraint sets) which are special cases of the original domain
(see Section 12.2 on page 324).
For example if the constraint set contains the condition A = B C. Domain splitting can be applied recursively to
obtain a tree of sub-domains of the original domain.
Once the user decides to stop the domain splitting, GATeL will produce a test
sequence for each sub-domain (if possible).
Summary
GATeL does not only allow to state invariance properties but allows to state
path predicates to express the test purpose. To support path predicates, GATeL
has to construct its test sequences backwards, i.e., it has to start with the final
state to be reached by the test sequence. Thus the test sequence is not generated
during the execution of the SUT, but before the SUT is executed.
This backward search is implemented in terms of a backtracking algorithm. The
backtracking algorithm has to guess appropriate assignments when the current
constraint set does not enforce a particular assignment or does not allows further
simplification.
Moreover, GATeL requires the SUT to be given as Lustre source code, representing
either the actual implementation or its complete specification. Again, this is
necessary, since GATeL has to construct its test sequences backwards.
The feature of domain splitting allows to further subdivide the domain of interesting
test sequences interactively. Moreover, it requires human intervention,
which does not allow to generate a large number of sub-domains automatically.
Finally, the domain splitting applies to the initial constraint set, which primarily
constrains the very last cycles of the test sequence. Consequently, the domain
splitting as implemented by GATeL only allows to split the domain wrt. the end
of the test sequence.