2 Why We Need Model-Based Testing

Advanced Topics 267
condition can be relaxed when the model program is used for on-the-fly testing with
observable actions.
Given a set of action symbols A, a model program is explorable for A if the
parameters of all the actions in A have finite domains in all states. For on-the-fly
testing with observable actions, the model program does not need to be explorable
for observable actions. The reason is that the arguments for the observable actions
are provided by the stepper. Recall that the fundamental property of model program
exploration is that it is lazy. During on-the-fly testing, an observable action is
executed in the model program only when it has occurred in the implementation, at
which point all the parameters have been provided.
Consider the model program SP[Credits,Commands,Setup] with the three included
features from Chapter 14. Notice that Cancel is not in the action vocabulary
of that model progam. Let us add another feature to SP that restricts the parameters
of all the request actions so that each request asks for 3 credits and the requests use
ids from the window of allowed message ids.
namespace SP
{
[Feature]
public static class ReqParams
{
readonly static Set C = new Set(3);
readonly static Set M() { return Credits.window; }
[Action("ReqSetup(m,c)")]
[Action("ReqWork(m,c)")]
static void Req([Domain("M")]int m, [Domain("C")]int c){ }
}
}
The model program SP[Credits,Commands,SetupModel,ReqParams] is explorable
for controllable actions but not for observable actions. Nevertheless, it is possible to
run ct with the following options, where SP.OTFTest.Make is a factory method for
this model program.
/r:SPImpl.dll /r:SP.dll SP.OTFTest.Make /iut:SPImpl.Stepper.Make
/o:ResWork /o:ResSetup
The following is a sample output that shows a conformance failure similar to the
one shown in Figure 16.1. Notice that the reason in the failure has been extracted
from the requirement attribute of the ResEnabled1 condition in Section 14.2.1 that
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