2 Why We Need Model-Based Testing

210 Testing Systems with Complex State
12.5 Advanced on-the-fly settings
The command-line utility ct is used throughout the book to illustrate how to run
conformance tests against an implementation under test. The utility can be configured
in several different ways, depending on the testing needs and requirements. In
this section we take a closer look at the main configuration options, some aspects
of the internal architecture, and some of the various extension points of the tool that
can be used to implement more advanced testing heuristics.
The modeling library can be used as a building block of a custom tool with
more advanced features than ct. In particular, the ConformanceTester class that is
used by ct has additional extension points that are not exposed through the settings
for ct, but can be accessed programmatically. The ct utility is implemented by
the static method RunWithCommandLineArguments of the ConformanceTester class
in the NModel.Conformance namespace. This method creates an instance of the
ConformanceTester class for a given stepper and strategy, configures its settings,
and invokes its Run method.
In the rest of this section we look at the following topics related to on-the-fly
testing. Most of the topics are illustrated by using various settings of ct.
• Specifying the model programs.
• Test execution and termination.
• The role of different kinds of actions.
• More on strategies.
– Using sampling.
– Using action weights to match operational profiles.
– Using state groupings to prune the search space.
12.5.1 Specifying the model programs
The main input to a model based on-the-fly testing algorithm is a model. In our
case a model is given by one or more model programs. A model program can be
provided either through a fully qualified name of a factory method, as a finite state
machines (FSM) (by using the fsm option of ct) or in the form of an offline test
suite (using the testSuite option). An FSM or an offline test suite is converted into
an equivalent model program. If several model programs are given, say m1, m2, and
m3, then they are composed into a single model program m = m1 ∗ m2 ∗ m3.
Composing several model programs together can be used for different purposes,
that has been illustrated on several occasions in previous chapters, and is discussed
in more detail in Chapter 14. It is always possible to provide a factory method that
creates a composed model program and one can provide that factory method as
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