2 Why We Need Model-Based Testing

75
Systems with Finite Models 109
TimeoutMsgLate()
76
73
Message("999.9") Command() TimeoutMsgLost()
74
ReportLostMessage()
102
78
83
105
107
6
Poll()
77
Calibrate()
Message("999.9")
72
7
10
2
3
0
Timeout() Command()
Reset()
Message("99.9") Command()
CheckMessage()
Timeout() Command()
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Message("99.9") TimeoutMsgLost()
Message("99.9") TimeoutMsgLate() Message("999.9")
100
101
104
NoHandler()
Command() Timeout()
Command()
Figure 6.10. Reactive system: interactive exploration showing path to unsafe state.
106
99
4
1
TimeoutMsgLate()
5
TimeoutMsgLost()
Liveness analysis depends on writing an accepting state condition that expresses
the goal we intend the program to achieve. An accepting state is often defined to be
a state where the program is allowed to stop. However, many programs including
embedded controllers (like the one in this example) are never supposed to stop. In
order to use liveness analysis with such systems, we must broadenour definition. We
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