public void AddRemoveHandlerTest()
        {
            var manager   = new WeakEventManager <EventArgs>();
            var validated = false;

            EventHandler <EventArgs> handler = (s, e) =>
            {
                Assert.Equal(s, this);
                validated = true;
            };

            manager.Add(handler);
            manager.Invoke(this, new EventArgs());

            Assert.True(validated);

            validated = false;
            manager.Remove(handler);
            manager.Invoke(this, new EventArgs());

            Assert.False(validated);
        }