2 Why We Need Model-Based Testing

274 Reactive Systems
The stepper consumes the events produced by the multiplexer, filters out the
resource usage events, and maps all the other events into observable actions that are
enqueued into the observation queue of the conformance tester.
Consider the example with two agents A1 and A2 depicted in Figure 16.7. A
possible sequence of events that are entered into the observation queue is
(a, e, b, c, f, g, d)
An asynchronous stepper can use a multiplexer to enqueue events into the observation
queue of the conformance tester. For example, in the stepper of the SP
server shown in Figure 16.5, if the different requests to the server always start different
threads that may share resources and the server supports per-thread response
handlers, then multiplexing of the thread-based events could be integrated into the
responder.
16.7 Exercises
1. Consider the revision control system model program in Chapter 10. What
actions are controllable and what actions are observable? Motivate.
2. Extend the sample SP server and stepper to handle cancellation and run ct to
experiment with it.
3. Define an FSM that accepts the closure Timeout() ∗ and compose it with the
model program SP[Credits,Commands,Setup] and Wait20 as defined in Section
16.5.1. What kind of test results do you expect when you run ct on this?
4. Write a adaptive strategy that tries to cover partially explored states as discussed
in Section 16.5.2 assuming that the IUT is determinisitic.
5. Implement the multiplexing algorithm discussed in Section 16.6.1.
6*. Implement a passive tester (as discussed in Section 16.5.3) that multiplexes
events from multiple log files.
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