Lecture Notes in Computer Science 3472

196 Machiel van der Bijl and Fabien Peureux
the observation of quiescence where it is not allowed according to the specification.
For outputs that are allowed, we continue the test derivation with
tx , tθ respectively.
Example. We illustrate the test derivation algorithm with our coffee machine
specification like the one shown on the left hand side in figure 7.6. We will show
how to derive an LTS with the algorithm. We use the same test case as used
to explain the test case definition, see Figure 7.10. When we start, the set S
consists of only the start state q1 of our specification. We choose one of the three
rules of the test derivation algorithm. Randomly, we start with applying rule 2 of
the test derivation algorithm and apply the input button. This is possible, since
q1 after button = {q2} (�= ∅). The result is the transition (t0, !button, t1) inour
test case. The set S is updated to S = {q2}. So we now have a test case with the
stimulus button. Now we choose to observe responses from the implementation
under test; we apply rule three. There are three possible responses: tea, coffee
and quiescence. We compute out(q1) ={δ} of the specification. So, the only
allowed output is quiescence. Therefore we add a transition with tea to a failstate
(t1, ?tea, t2) and a transition with coffee to a fail state (t1, ?coffee,t4).
For the allowed response δ we add the transition (t1,θ,t3). We update S with
S after δ = {q2}. We again apply the stimulus button which results in the
transition (t3, button, t5) andS = {q3}. For rule 3 there are now two options,
either the response coffee or tea, since out(q2) ={coffee, tea}. We can add the
transitions (t5, ?tea, t6), (t5, ?coffee,t8) and(t5,θ,t7) wheret7 is a fail-state.
Because of non-determinism in the specification we have two possible paths to
continue with. For the “tea” path we update S with {q5} and for the “coffee”
path we update S with {q4}. We can in principle continue forever with choosing
between step 2 and three of the test derivation algorithm until we reach a final
state in the specification or until we want to stop. In our case the specification
has reached a final state and we can apply rule 1 to stop the recursion. This
transforms states t6 and t8 into pass-states.
7.5.1 Conformance Testing Based on Input/Output State Machine
In practice, system testing is performed with test suites. Each test case of a test
suite is defined to verify that a specific property of the specifications is correctly
implemented, or to detect a precise fault in the implementation. A test case
can be seen as a finite sequence of interactions between a tester and the tested
implementation. This process ends by the assignment of a verdict (usually pass,
fail or inconclusive).
The method of conformance testing introduced by M. Phalippou on IOSM is
different [Pha93]. Indeed, his idea consists in considering in a global way the set
of all interactions and sequences of interactions between the tester and the tested
implementation. According to this principle, a unique object, called canonical
tester, is defined to represent in the one hand all the executions performed by a
given test suite, and in the other hand all its execution.