2 Why We Need Model-Based Testing

82 Model Programs
the set of argument values for the parameter. When a tool executes the action method,
it will choose one element from this set to assign to that parameter. A domain can
also be a field or a property. The domain can depend on the state (it can return
different sets of values in different states).
static Set Temperatures()
{
return new Set(Temp1, Temp2);
}
Here the domain method always returns the same set. A domain method can return a
set that is computed from the state. Set is a C# generic collection type that is provided
by the modeling library (Chapter 10). Here identifies the type of the
elements of the set, which must match the type of the parameter in the action method.
In this example we code the domain in the model. In Chapter 7 we show how to
code the domain separately from the model (which makes it easier to use different
domains with the same model).
Now that we have a model program, we must validate it. Since we intend to use
it for testing, we must show that it behaves as the implementation is supposed to
behave. We can do a few simulation runs as we did in Section 5.5, simulating the
test run of Chapter 2, Section 2.8, for example. We will analyze this model program
more thorougly in Chapter 6 and use it to generate and check tests in Chapter 8.But
first we present another model program.
5.7 Case study: reactive program
In this section we model the reactive system discussed in Chapter 3. This example
shows how a single model program can represent a reactive program interacting
with its environment.
5.7.1 Preliminary analysis
Purpose
The purpose of this model program is to be the subject of a design analysis that
can reveal the design errors that we discovered by testing in Chapter 3, Sections 3.4
and 3.5.
We also plan to use this model program for testing. After the design errors are
corrected in the model program, we will be able to use the corrected model program
to generate and check tests for the revised implementation (which still might have
defects).
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