2 Why We Need Model-Based Testing

262 Reactive Systems
namespace BagModel
{
[Feature]
static class Draw
{
static Bag B { get { return Contract.content; } }
static bool drawing = false;
[Action]
static void Draw_Start() { drawing = true; }
static bool Draw_StartEnabled() { return !drawing && !B.IsEmpty; }
[Action]
static void Draw_Finish([Domain("B")]string e)
{ drawing = false; Contract.content = B.Remove(e); }
static bool Draw_FinishEnabled(string e)
{ return drawing && B.Contains(e); }
[Action("Add"), Action("Delete")]
[Action("Lookup_Start"), Action("Lookup_Finish")]
[Action("Count_Start"), Action("Count_Finish")]
static void Other() { }
static bool OtherEnabled() { return !drawing; }
}
}
Figure 16.2. A dependent Draw feature for BagModel in Figure 12.2.
stepping. In other words, queueing of obsevable actions is not needed. In this case,
nondeterminism is resolved immediately when it occurs. Synchronous stepping, as
discussed in Section 12.2.3, is then an adequate solution to harness the IUT for
testing.
Shallow nondeterminism. In some cases, nondeterminism arises only because of
multiple possible outputs to some inputs. In particular, all states of the model program
are such that either all enabled actions in a state are controllable or all enabled actions
in a state are observable. Say a state is active in the first case and passive in the
second case. Moreover, a transition from a passive state leads to an active state.
To illustrate this case on a concrete example, recall the bag example from Chapter
12. Suppose that a dependent feature called Draw is added to the bag model
program that allows elements to be chosen and removed (drawn) from the bag (see
Figure 16.2).
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