I wanted to try a little design by contract in my latest C# application and wanted to have syntax akin to: public string Foo() { set { Assert.IsNotNull(value); Assert.IsTrue(value.Contains("bar")); _foo = value; } } I know I can get static methods like this from a unit test framework, but I wanted to know if something like this was already built-in to the language or if there was already some kind of framework floating around. I can write my own Assert functions, just don't want to reinvent the wheel.