2 Why We Need Model-Based Testing

44 Why We Need Model-Based Analysis
?Timeout, Message, OK
ReportLostMessage
?Command, Timeout, OK
Calibrate ’99.9’
?Timeout, Timeout, OK
Poll
?Message ’99.9’, Message, OK
CheckMessage ’99.9’, compare to 99.9, OK
?Command, Timeout, OK
Calibrate ’99.9’
?Exit, Timeout, OK
Did the expected handlers run? [y/n] y
Tests run: 1, Failures: 0, Not run: 0, Time: 8.606 seconds
These tests confirm that the controller works as intended in these runs. Can we
conclude from this that the controller will always work?
3.4 Failures in simulation
We experiment with the simulator and find that the controller does not always behave
as we intend. Recall that we intend that a calibrate command will be carried out if
the most recent sample from the sensor is within-range, but will not be carried out
if the most recent sample is out-of-range. We also intend that the controller should
not experience any generic failures such as program crashes (unhandled exceptions
in .NET), deadlocks, or endless cycles that get nowhere. Despite our intentions,
we observe examples of all of these (which we can reproduce by coding unit
tests).
In this run, CommandWhenWaiting, a calibrate command is ignored even though the
sensor is OK. The command arrives when the controller is waiting for a message;
no handler runs.
?Timeout, Timeout, Error
Reset
?Message ’99.9’, Message, Error
CheckMessage ’99.9’, compare to 99.9, OK
?Timeout, Timeout, OK
Poll
?Command, Message, OK
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