public void Cancel()
        {
            Assert.True(CancellationHelper.Cancel(ref _cts));

            Assert.Same(_cts, CancellationHelper.Cancelled);

            Assert.False(CancellationHelper.Cancel(ref _cts));
        }
        public void Replace_After_Cancel()
        {
            Assert.True(CancellationHelper.Cancel(ref _cts));

            var cts = new CancellationTokenSource();

            Assert.False(CancellationHelper.Replace(ref _cts, cts));

            Assert.True(cts.IsCancellationRequested);
        }