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Spec Explorer is a Model-Based Testing (MBT) tool from Microsoft. It extends the Visual Studio Integrated Development Environment with the ability to define a model describing the expected behavior of a software system. From these models, the tool can generate tests automatically for execution within Visual Studio's own testing framework, or many other unit testing frameworks.
The name Spec Explorer comes from its power to explore these models (aka specifications) in order to discover all the potential behaviors they define, and present a graphical view of the result. Although the outcome of an exploration can be huge, the Cord language provides a very intuitive way to reduce it by selecting scenarios relevant for testing. This proves to be a very effective way to deal with the notorious state explosion problem.