2 Why We Need Model-Based Testing

ShowText()
Systems with Finite Models 101
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SortByFirst()
4
ShowTitles()
SelectMessages() SelectTopics()
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ShowTitles()
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SortByMostRecent()
SelectMessages()
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ShowText()
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SelectMessages() SelectTopics()
SelectMessages() SelectTopics()
SelectTopics()
Figure 6.4. Newsreader true FSM: state transition diagram drawn by mpv tool.
It can be helpful to view the graph produced by exploration even when you do
not have a precise question in mind, because it might reveal that the model program
does not behave as you intend. For example, you may see many more or many fewer
states and transitions than you expected, or you may see dead ends or cycles you
did not expect.
We recommend that you explore and view your model program as you develop
it, so you can check frequently that it behaves as you intend. There is no need to
finish the model program first; you can begin exploring as soon as you have coded
a few actions.
6.2.3 Interactive exploration and simulation
The mpv tool can also explore interactively, executing and displaying a few transitions
at a time, under the user’s control. This provides a more convenient way to simulate
particular runs than coding and executing main methods or unit tests, as we did in
Chapter 5, Section 5.5
Figures 6.5 and 6.6 show the interactive exploration of the first run we tested in
Chapter 5. At first, only the initial state appears. At our command, mpv shows all the
actions enabled in the initial state. We select ShowTitles by selecting its next state
(Figure 6.5). Then we command mpv to show all the transitions enabled in that state,
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