public async Task ExecuteAsyncFailureTest()
        {
            SlackNotifyOperation op = new SlackNotifyOperation();

            op.WebhookURL = WehookURL;
            op.Channel    = "#channel-doesnt-exist";
            op.Message    = "This is a test message run from a unit test in BuildMasterExtension.SlackNotifyOperationTests";

            var ex = await AssertEx.ThrowsAsync(() => op.ExecuteAsync(new ContextStub()));
        }
        public async Task ExecuteAsyncTest()
        {
            SlackNotifyOperation op = new SlackNotifyOperation();

            op.WebhookURL = WehookURL;
            op.Channel    = "#general";
            op.Message    = "This is a test message run from a unit test in BuildMasterExtension.SlackNotifyOperationTests";

            await op.ExecuteAsync(new ContextStub());
        }