public void when_installing()
        {
            var extensionHost  = Substitute.For <IExtensionHost>();
            var extensionPoint = extensionHost.GetExtensionPoint("TestDecorators");

            var result = addin.Install(extensionHost);

            specify(() => result);

            specify(() => extensionPoint.Received().Install(Arg.Any <NSpecTestDecorator>()));
        }