Visual Studio 2012 has plenty of unit testing features.
NServiceBus.Testing offers testing by sending messages through message handlers and sagas. This includes anything that a message handler and saga can do, including header manipulation and dependency injection. You can visit http://docs.particular.net/NServiceBus/unit-testing for some basic examples. For the source code of
NServiceBus.Testing, visit https://github.com/Particular/NServiceBus/tree/develop/src/NServiceBus.Testing.
The very basics of starting unit testing is to create a unit test project in Visual Studio by adding a new unit test project to an existing solution. See http://msdn.microsoft.com/en-us/library/hh598957.aspx/ for details.
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