2 Why We Need Model-Based Testing

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Advanced Topics 263
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Add("b")
Draw_Start()
Add("a")
2
Add("b")
Draw_Start()
10
6
1
Draw_Finish("a")
Draw_Finish("b")
0
Add("a")
Draw_Start()
Draw_Finish("b")
Draw_Finish("a")
8
0
Add("a") Draw() / "a"
1
Add("b") Draw() / "b"
3
Draw() / "a" Add("a")
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Add("b") Draw() / "b"
(a) (b)
Figure 16.3. Partial exploration of BagModel[Draw]. In (b) passive states are hidden.
The model program has two new actions Draw Start() and Draw Finish(e),
where the first action represents a request to draw and the second action represents
a particular element e that was drawn. This action is nondeterministic because any
element in the bag might be drawn (any element from the domain B might be chosen).
The state variable drawing is used to disable all actions besides Draw Finish until
the draw operation has been completed.
A partial exploration of BagModel[Draw] with mpv is illustrated in Figure 16.3.All
passive states are shown as diamonds in Figure 16.3(a). (The mpv tool can generate
a partial exploration interactively, as described in Chapter 6, Section 6.2.3.) The
nondeterminism is indicated by the two Draw Finish transitions exiting from state 6
in Figure 16.3(a) and the two Draw transitions exiting from state 3 in Figure 16.3(b).
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