Lecture Notes in Computer Science 3472

14 Tools for Test Case Generation 399
14.2.2 Lurette
Introduction
The approach of Lurette3 is generally comparable to Lutess which has been
presented above [RNHW98]. Lurette is also based on the synchronous dataflow
language Lustre. Both tools build their test harness from three elements, namely
the SUT, a test sequence generator, and an oracle. Moreover, both tools derive
the test sequence generator from an environment description written in Lustre
while the SUT is tested as a black box. Finally, both tools utilize environment
descriptions and oracles given as synchronous observers. Synchronous observers
are programs which implement acceptors for sequences. A synchronous observer
used as environment description will output true as long as the sequence presented
to the observer represents a valid sequence of events in the environment.
However, in contrast to Lutess, Lurette allows to validate systems which
have numerical inputs and outputs. On the other hand, Lurette is only offering
a single mode for test sequence generation. The randomly generated sequences
are based on a uniform distribution. Also, Lurette requires that the SUT is given
as a C-file which implements a predefined set of procedures.
The test sequence is generated on the fly during the execution of the SUT.
An initial input is provided by the test sequence generator and fed into SUT.
From then on, the SUT and the test sequence generator compute outputs and
inputs in an alternating fashion.
Testing Method
The testing method of Lurette is relatively simple. The environment description
is used to express both relevant and interesting test sequences. In [RNHW98],
the term relevance refers to those properties which constrain the environment
itself and the term interest refers to the test purpose. The constraints which represent
the relevance and the interest are expressed within the same synchronous
observer, i.e., there is no distinction between the environment description and
the test purpose. This observer is fed with the inputs and outputs of the SUT
and evaluates to true, if the sequence so far is relevant and interesting.
A test sequence generated by Lurette is constructed uniformly and randomly
such that the observer evaluates to true in every single step of the sequence.
In other words, Lurette has to invert the environment description to compute a
new input vector for the SUT based on the current state of the environment and
the last output of the SUT. The oracle is also fed with the inputs and outputs
of the SUT to evaluate the correctness of the sequence. The result of the oracle
is either a fail or pass verdict.
Test Sequence Generation
In each step of the test sequence generation, Lurette has to compute an input
vector for the SUT based on the internal state of the environment description
3 See also http://www-verimag.imag.fr/SYNCHRONE/lurette/lurette.html.