2 Why We Need Model-Based Testing

268 Reactive Systems
refers to the part of the natural language document that specifies the condition that
clients must not starve.
TestResult(7, Verdict("Failure"),
"Action ’ResWork(1, 0, Status(\"Completed\"))’ not enabled in the model
Section ...: Client must have enough credits",
Trace(
ReqSetup(0, 3),
ResSetup(0, 1, Status("Completed")),
ReqWork(1, 3),
ResWork(1, 0, Status("Completed"))
)
)
16.5 Adaptive on-the-fly testing
Recall the test execution algorithm from Section 12.5.2. The top-level loop of the
adaptive version of the algorithm remains the same. The algorithm RunTest that
executes a single test run is extended here to handle the presence of observable
actions. The outline of the algorithm is shown in Figure 16.6 and follows very
closely the actual implementation in NModel. The extensions, that are emphasized
in Figure 16.6, affect only a few places in the code.
In the conformance tester a Boolean variable isAsync indicates if the operation
mode is asynchronous. There is an additional variable called obs that is an observation
queue or a queue of observable actions. The observation queue is of type
TimedQueue that is defined in the NModel.Algorithms namespace. When a
conformance tester is created for a given asynchronous stepper, the stepper is called
with SetObserver(obs.Enqueue) to initialize the observer in the stepper with the
method that enqueues actions into the observation queue.
When the observation queue is nonempty, the next observation is dequeued
from it and conformance to the model program is validated by using the strategy.
If the observation queue is empty, a controllable (tester) action is selected using
the strategy. If no tester action is enabled in the current state of the strategy, the
conformance tester waits for an observable action to arrive within a time limit of
obsTimeout milliseconds.
16.5.1 Wait and time-out actions
When the conformance tester is executed in the asynchronous mode, it uses two
auxiliary actions. The wait action is an internal action that is used when there are no
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