2 Why We Need Model-Based Testing

Systems with Complex State 185
relation does the modified model program have to the original? Mixing parameter
restrictions inline with our model confuses the contract (the system’s specified
behavior) with a scenario (a particular situation of interest for analysis or testing).
A better way to deal with this case would be to use the Feature attribute we saw
in Section 7.2. To do this, we create a new class within the same namespace:
namespace Counter
{
[Feature]
static class SmallDomain
{
readonly Set inputs = new Set(0, 1, 2, 3, 4);
}
}
[Action]
static void ModularIncrement([Domain("inputs")] int x) { }
We can combine the SmallDomain feature with the contract model program by means
of a factory method. Factory methods were introduced in Section 6.2.1.
namespace Counter
{
public static class Factory
{
public static ModelProgram Create()
{
return new LibraryModelProgram(typeof(Factory).Assembly,
"Counter", Set.EmptySet);
}
}
}
public static ModelProgram CreateFinite()
{
return new LibraryModelProgram(typeof(Factory).Assembly,
"Counter", new Set("SmallDomain"));
}
The factory contains methods that create either of two versions of the Counter
model. The model program produced by CreateFinite includes the feature that
restricts the domain to five elements. The advantage of this approach is that it keeps
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