2 Why We Need Model-Based Testing

192 Testing Systems with Complex State
On-the-fly testing with a programmable strategy is the testing technique supported
by the ct tool. Internally, it even handles offline testing (as demonstrated in
Chapter 8) as a special case of this.
12.1 On-the-fly testing
First let us demonstrate on-the-fly testing with the client/server example from previous
chapters. On-the-fly testing is the easiest way to begin testing with the ct
(Conformance Tester) tool. It is not necessary to generate a test suite or create a
scenario. All you need is an implementation (Chapter 2), a model program (Chapter
5), and a test harness or stepper (Chapter 8). The built-in strategy of the ct tool
is random testing: in each state, select an enabled action at random. (The strategy is
not completely random; it uses the model program to rule out actions that are not
enabled in the current state.) We know that this model program will always reach a
deadlock state or an accepting state, so we don’t have to make any arrangements to
stop the test runs. Let’s see if random testing can reveal the defect we know is there.
We issue this command:
ct /r:ClientServer.dll ClientServer.Factory.Create
/r:Stepper.dll /iut:ClientServerImpl.Stepper.Create
/runs:1
One test run executes:
TestResult(0, Verdict("Failure"),
"Run stopped in a non-accepting state",
Trace(
ClientSocket(),
ServerSocket(),
ServerClose()
)
)
The tester randomly chose one of the many paths to a deadlock state (state 9 in
Figure 7.2 in Chapter 7). This happens again and again, so we give ct some guidance
by providing a scenario machine (Figure 7.14 in Chapter 7).
ct /r:ClientServer.dll ClientServer.Factory.Create
/r:Stepper.dll /iut:ClientServerImpl.Stepper.Create
/runs:1
/fsm:Scenario.txt
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