2 Why We Need Model-Based Testing

Systems with Finite Models 67
5.4.1 Program structure
A model program must include using statements to use the namespaces of the modeling
library NModel. A typical model program uses the NModel, NModel.Attributes,
and NModel.Execution namespaces. All of these are provided by the library
NModel.dll. A model program is compiled to a library, for example, by a command
like this one (where DEVPATH is an environment variable that stores the path to
the directory that contains the library, e.g., C:\Program Files\NModel\bin):
csc /t:library /r:"%DEVPATH%\NModel.dll" NewsReaderUI.cs
We code each model program in its own namespace. A model program consists
of the actions and variables defined by the types declared in its namespace. The
namespace name is the model program name: NewsReader in this example. A model
program can include more than one class (or other types); this simple example has
just one class.
NewsReader declares some variables to store the state, some methods to implement
the actions, and some methods to test when each action is enabled. That’s all there
is to a model program. A model program does not have a main method or any other
control structure for invoking the actions.
We recommend coding model programs with no access modifiers, so most types
and members have the default private access. The tools can access private types and
members (using a mechanism we will describe in Chapter 6).
5.4.2 State variables
The state variables of the model program are the static fields and instance fields declared
in the model program’s namespace. Public and nonpublic fields are included.
Fields inherited from base classes (outside of the model namespace) are included.
In our example there are only three state varables. Each has only a few values so
we declare an enumerated type for each.
enum Page { Topics, Messages };
enum Style { WithText, TitlesOnly };
enum Sort { ByFirst, ByMostRecent };
In our examples all of the state variables are static variables. We declare all three,
and assign the initial state in the declarations.
static Page page = Page.Topics;
static Style style = Style.WithText;
static Sort sort = Sort.ByMostRecent;
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