public void TestFireOnce()
        {
            int ea = 0;
            EventHandler <EventArgs> eventWithArgs = (sender, args) => ea++;

            Delegates.AttachWithUnsubscribe(this, nameof(DelegateTests.TestEventArgs), eventWithArgs);

            TestEventArgs?.Invoke(this, null);
            TestEventArgs?.Invoke(this, null);
            TestEventArgs?.Invoke(this, null);

            ea.ShouldBeEquivalentTo(1);
            TestEventArgs.Should().BeNull();
        }