Lecture Notes in Computer Science 3472

14 Tools for Test Case Generation 395
vectors, then the complete test sequence can be reproduced based on the initial
random seed given to the test sequence generator.
Lutess is aimed at two goals – first it supports a monoformalistic approach,
i.e., the software specification, the test specification and the program itself can be
stated in the same programming language. Second, the same technology should
support verification and testing techniques [dBORZ99].
Lustre
Lustre is a high-level programming language for reactive systems [HCRP91,
CPHP87] which combines two main concepts, namely it is a dataflow oriented
as well as a time-synchronous language.
Lustre is based on the synchrony hypothesis, i. e., a Lustre program is written
with the assumption that every reaction of the program to an external event is
executed instantaneously. In other words, it is assumed that the environment
does not change its state during the computation of a reaction. This allows the
use of an idealized notion of time where each internal event of a program takes
place at a known point in time with respect to the history of external events.
To make this concept usable in practice, Lustre is designed such that each
Lustre program can be compiled into a finite IO-automaton where each state
transition is compiled into a piece code without branches. A transition of this
automaton corresponds to an elementary reaction of the program. Thus, it is
possible to give an accurate upper bound on the maximum reaction time of the
program for a given machine. This structuring of compiled synchronous programs
was introduced in the context of the Esterel language [BC85]. Taken together,
this approach allows to check the synchrony hypothesis.
Many reactive systems are easily and naturally modeled in terms of dataflows.
Each dataflow is a mapping of discrete time to values, i.e., a dataflow X represents
a sequence of values x1, x2,.... In Lustre, reactive systems are composed
of flows of data which are recombined and transformed by a set of operators. In
fact each variable in Lustre represents a dataflow. So for example, in Lustre the
statement X = Y + Z means that each element of the flow X equals the sum
of the corresponding elements of the flows Y and Z , i.e., if Y = y1, y2,... and
Z = z1, z2,... then X = x1, x2,... with xi = yi + zi.
Advantages of the dataflow approach are that it is functional and parallel.
Functional programs are open to automated analysis and transformation because
of the lack of side-effects. Parallel components are naturally expressed in Lustre
by independent dataflows. Synchronization is implicitly described by data
dependencies between the different dataflows.
The following piece of code implements a counter as a so called node. 1 A
node recombines a set of dataflows into a new one. In this case val init is used
as initialization of the new flow which is then incremented by val incr in each
cycle.
1 This example has been taken from [HCRP91].