TempData

_controller.Index();

_controller.ShouldHaveTempDataProperty("Message")
_controller.ShouldHaveTempDataProperty("Message", "Welcome to the website.")
_controller.ShouldHaveTempDataProperty<string>("Message", m => m.Contains("Welcome"))

It is important to note that the compiler cannot infer the generic type argument based on the given lambda expression and so you must explicitly supply a generic type argument in all cases.

It may also be important to note that the temp data test methods break the convention slightly by defining test methods directly on the Controller instead of on the immediate result of WithCallTo. This is slightly counter-intuitive at first, but ultimately, it enables you to be more dynamic when writing your tests.