A Windows application is a non-Web based program which runs on a user’s machine. Microsoft Excel is a good example of a Windows application. In general you can identify Windows applications because they usually have menu items File, Edit, View, and so on. Except for very simple programs, Windows application programs are composed of building blocks called DLLs (dynamic link libraries). The most fundamental type of Windows application testing is the process of testing these building blocks. This is usually called unit testing, or API testing. The idea is quite simple. If the individual building blocks of a software system are not correct, the system as a whole cannot be correct. For example, suppose developers are creating a cribbage game program. Behind the scenes there is likely to be a DLL which calculates the point value of various card combinations. The image below shows an example of a test run which tests this DLL building block.