Lecture Notes in Computer Science 3472

7 I/O-automata Based Testing 195
Definition 7.34. Let s ∈LTS(I , U ) be a specification with initial state q0.
Let S be a non-empty set of states, with initially S = {q0}. A test case t ∈
TEST (U ∪{θ}, I ) is obtained from S by a finite number of recursive applications
of one of the following three non-deterministic choices:
(1) pass
(2)
(3)
t := pass
Thetestcasewithonlythestatepass is always a sound test case. This
rule stops the recursion in the algorithm.
a
✁❆
✁ t ❆❆
✁
′
t := a; t ′ where a ∈ I , S after a �= ∅ and t ′ is obtained by recursively applying
the algorithm for S ′ = S after a.
This step in the algorithm adds an input action a to the test case. After applying
the input a, the test case behaves as t ′ which is obtained by applying
the test derivation algorithm recursively to S ′ . t ′ is depicted as an abstract
subtree (triangle) in the figure above.
x1 x2 x3 θ
fail fail
✂❇
✂ ❇❇❇❇
t1 ✂
✂✂
✂❇
✂ ❇❇❇❇
t2 ✂
✂✂
t := Σ {x; fail | x ∈ U , x �∈ out(S)}
+ Σ {θ; fail | δ �∈ out(S)}
+ Σ {x; tx | x ∈ U , x ∈ out(S)}
+ Σ {θ; tθ | δ ∈ out(S)}
where tx and tθ are obtained by recursively applying the test derivation algorithm
for S ′ = S after x , S after δ, respectively. In this definition + and
Σ have the standard process algebraic meaning. + stands for choice and Σ
stands for the sum of all expressions in a set.
In this step we add expected outputs to the test case. If the output is incorrect
according to the specification we add a transition with the output
to a fail state, thus ending that part of the test case. The same holds for