2 Why We Need Model-Based Testing

Overview 23
control structure (sequences, loops, and conditional statements) that implement our
protocol, and also provide data (such as IP addresses and port numbers) used by the
libraries.
When an application is compiled, it references the libraries it uses: the compiler
consults the library assemblies for information it needs. This command compiles
the Monitor application, which uses the Server and Temperature libraries.
csc /target:exe /reference:Server.dll,Temperature.dll Monitor.cs
In the .NET framework, an application is an assembly that contains a main
method. It has the file type exe. The application assembly does not contain the
compiled code of the libraries it uses. Instead, it loads those library assemblies
when it is executed. The referenced libraries must be available when the application
is compiled, and again when it is executed. 1
This concludes our description of the remote instrument software. Now we can
describe our testing and analysis.
2.6 Unit testing
We begin our testing and analysis with unit testing. Testing checks software by
executing it. The software that is tested is called the implementation under test
(IUT). Different kinds of testing can be distinguished by the amount of software
that is included in the IUT. System testing executes entire applications, such as our
Logger or Monitor programs. Unit testing executes some of the parts, or units, from
which applications are built. In C#, the units are classes or other types. When we
are doing unit testing in the .NET framework, the IUT is a library (or libraries),
such as our Client and Server libraries. Creating and running unit tests require
familiarity with the source code and access to the same files and tools that the
developers use. Typically, unit testing is done by the same developers who write the
code.
For this example we use the NUnit testing tool, the .NET member of the xUnit
family that also includes JUnit (for Java), CppUnit (for C++), and several others. 2
NUnit provides a library for writing tests, which defines several attributes and
assertions. NUnit also provides test runner applications that execute the tests and
report the results.
1 There are many options for locating libraries: they can be in the same directory as the application,
or in a special .NET directory called the Global Assembly Cache (GAC), or in a directory
identified by one of the .NET .config files.
2 Some editions of Microsoft Visual Studio include a similar unit testing tool.
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