While using Gallio for performing Unit Tests within Visual Studio, I have noticed that some times you can't run Unit Tests, or it says that no tests available, with thanks to Lee, he pointed me to a simple fix

Visual Studio can be used to run your tests in process, with the debugger. In order for a project to be “testable”, you'll need to make sure it has the following in the csproj:

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<ProjectTypeGuids>{3AC096D0-A1C2-E12C-1390-A8335801FDAB};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>