public void StaticCompositeSubscription_AddRemove_Throws()
        {
            var cs = new StaticCompositeSubscription();

            var s1 = new MySub();

            Assert.ThrowsException <InvalidOperationException>(() => cs.Add(s1));

            var cs2 = new StaticCompositeSubscription(s1);

            Assert.ThrowsException <InvalidOperationException>(() => cs.Remove(s1));
        }