We just released the version 0.20 of Pex. This version brings a Beavers, an extension of Stubs to write models, a global event view in Visual Studio and many bug fixes. Beavers are a small programatic models that build upon Moles…

• Beavers: With stubs and moles, we provided a framework to write record/replay tests (i.e. mock-based tests) against any .NET type, interface or not. Beavers take you to the next level and allow you to write simple implementations with behavior (hence the ‘B’eaver) that can be used to replace the external system during testing. The benefit of using Beavers is that the resulting test cases are much more robust to code changes since the tests specify the state of the system, rather than a sequence of method calls and outcomes. We will talk a lot about Beavers in the future. Let’s take a look at an example. The following snippet uses Moles to redirect the constructor of a Bank class, then sets up the GetAccountById(int) method to return an instance of IAccount, etc… This is a typical test that is based record and replay. The problem with this technique is that it is really fragile with respect to code changes: if the code calls different methods, the test will break.