2 Why We Need Model-Based Testing

110 Exploring and Analyzing Finite Model Programs
[AcceptingStateCondition]
public static bool SafeCalibrateEnabled()
{
return (CalibrateEnabled()
&& buffer == InRange
&& previous == double.Parse(InRange));
}
Figure 6.11. Reactive system: accepting state condition for liveness analysis.
now say that an accepting state is a state where a program goal has been achieved,
where some unit of work has been finished, where there is not a portion of work
left undone, where a task has been completed, and where there is not some task left
unfinished. Some judgment and understanding of a program’s purpose is required
in order to identify its accepting states.
Recall that the purpose of our reactive system is to perform a calibration with a
valid temperature sample. Also recall that a temperature sample is considered valid
when it does not differ too much from the preceding sample. Therefore, the goal
of the program has been achieved when two successive within-range temperatures
have been sampled, and a Calibration action occurs. Liveness analysis requires that
we express this in terms of a state, not an action, so once again we subsitute the
action’s enabling condition for the action itself. The accepting state condition is
CalibrateEnabled() && buffer == InRange
&& previous == double.Parse(InRange)
We wrap this expression in a static method, label it with the [AcceptingStateCondition]
attribute, and place it in the Controller class in the Reactive model program
namespace (Figure 6.11).
Now that we have defined the accepting state condition, exploration can find all
of the accepting states and dead states in the generated FSM. We command the mpv
tool to explore the reactive system model program, and to count and display unsafe
states:
mpv /r:Controller.dll Reactive.Factory.Create /livenessCheckIsOn+ ...
Figure 6.12 shows the generated FSM. We had to increase MaxTransitions to
300 to generate the true FSM. The mpv tool finds 239 transitions and 121 states,
including 2 accepting states and 61 dead states. The accepting states are marked but
they are hard to find in Figure 6.12. They are easier to find in the mpv session, where
we can magnify and scroll the graph.
The dead states are easier to find, because there are so many of them. Near the
initial state, the FSM divides into two regions, each with many interior links but no
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