public void Should_validate_length() { var ok1 = new Model { MyProperty = null }; var ok2 = new Model { MyProperty = "" }; var ok3 = new Model { MyProperty = "55555" }; var fail = new Model { MyProperty = "1" }; var v = new ModelValidator(); v.ValidateAndThrow(ok1); v.ValidateAndThrow(ok2); v.ValidateAndThrow(ok3); Should.Throw <ValidationException> (() => v.ValidateAndThrow(fail)); }