public static void PredictInput()
        {
            const string Input = "Hello world";
            MyPredictor  slow  = MyPredictor.SlowPredictor;
            MyPredictor  fast  = MyPredictor.FastPredictor;
            Ast          ast   = Parser.ParseInput(Input, out Token[] tokens, out _);

            // Returns null when no predictor implementation registered
            List <PredictionResult> results = CommandPrediction.PredictInput(Client, ast, tokens).Result;

            Assert.Null(results);

            try
            {
                // Register 2 predictor implementations
                SubsystemManager.RegisterSubsystem <ICommandPredictor, MyPredictor>(slow);
                SubsystemManager.RegisterSubsystem(SubsystemKind.CommandPredictor, fast);

                // Expect the results from 'fast' predictor only b/c the 'slow' one
                // cannot finish before the specified timeout.
                // The specified timeout is exaggerated to make the test reliable.
                // xUnit must spin up a lot tasks, which makes the test unreliable when the time difference between 'delay' and 'timeout' is small.
                results = CommandPrediction.PredictInput(Client, ast, tokens, millisecondsTimeout: 1000).Result;
                Assert.Single(results);

                PredictionResult res = results[0];
                Assert.Equal(fast.Id, res.Id);
                Assert.Equal(Session, res.Session);
                Assert.Equal(2, res.Suggestions.Count);
                Assert.Equal($"'{Input}' from '{Client}' - TEST-1 from {fast.Name}", res.Suggestions[0].SuggestionText);
                Assert.Equal($"'{Input}' from '{Client}' - TeSt-2 from {fast.Name}", res.Suggestions[1].SuggestionText);

                // Expect the results from both 'slow' and 'fast' predictors
                // Same here -- the specified timeout is exaggerated to make the test reliable.
                // xUnit must spin up a lot tasks, which makes the test unreliable when the time difference between 'delay' and 'timeout' is small.
                results = CommandPrediction.PredictInput(Client, ast, tokens, millisecondsTimeout: 4000).Result;
                Assert.Equal(2, results.Count);

                PredictionResult res1 = results[0];
                Assert.Equal(slow.Id, res1.Id);
                Assert.Equal(Session, res1.Session);
                Assert.Equal(2, res1.Suggestions.Count);
                Assert.Equal($"'{Input}' from '{Client}' - TEST-1 from {slow.Name}", res1.Suggestions[0].SuggestionText);
                Assert.Equal($"'{Input}' from '{Client}' - TeSt-2 from {slow.Name}", res1.Suggestions[1].SuggestionText);

                PredictionResult res2 = results[1];
                Assert.Equal(fast.Id, res2.Id);
                Assert.Equal(Session, res2.Session);
                Assert.Equal(2, res2.Suggestions.Count);
                Assert.Equal($"'{Input}' from '{Client}' - TEST-1 from {fast.Name}", res2.Suggestions[0].SuggestionText);
                Assert.Equal($"'{Input}' from '{Client}' - TeSt-2 from {fast.Name}", res2.Suggestions[1].SuggestionText);
            }
            finally
            {
                SubsystemManager.UnregisterSubsystem <ICommandPredictor>(slow.Id);
                SubsystemManager.UnregisterSubsystem(SubsystemKind.CommandPredictor, fast.Id);
            }
        }
        public static void Feedback()
        {
            MyPredictor slow = MyPredictor.SlowPredictor;
            MyPredictor fast = MyPredictor.FastPredictor;

            try
            {
                // Register 2 predictor implementations
                SubsystemManager.RegisterSubsystem <ICommandPredictor, MyPredictor>(slow);
                SubsystemManager.RegisterSubsystem(SubsystemKind.CommandPredictor, fast);

                var history = new[] { "hello", "world" };
                var ids     = new HashSet <Guid> {
                    slow.Id, fast.Id
                };

                CommandPrediction.OnCommandLineAccepted(Client, history);
                CommandPrediction.OnSuggestionDisplayed(Client, slow.Id, Session, 2);
                CommandPrediction.OnSuggestionDisplayed(Client, fast.Id, Session, -1);
                CommandPrediction.OnSuggestionAccepted(Client, slow.Id, Session, "Yeah");

                // The calls to 'StartEarlyProcessing' and 'OnSuggestionAccepted' are queued in thread pool,
                // so we wait a bit to make sure the calls are done.
                while (slow.History.Count == 0 || slow.AcceptedSuggestions.Count == 0)
                {
                    Thread.Sleep(10);
                }

                Assert.Equal(2, slow.History.Count);
                Assert.Equal($"{Client}-{history[0]}", slow.History[0]);
                Assert.Equal($"{Client}-{history[1]}", slow.History[1]);

                Assert.Equal(2, fast.History.Count);
                Assert.Equal($"{Client}-{history[0]}", fast.History[0]);
                Assert.Equal($"{Client}-{history[1]}", fast.History[1]);

                Assert.Single(slow.DisplayedSuggestions);
                Assert.Equal($"{Client}-{Session}-2", slow.DisplayedSuggestions[0]);

                Assert.Single(fast.DisplayedSuggestions);
                Assert.Equal($"{Client}-{Session}--1", fast.DisplayedSuggestions[0]);

                Assert.Single(slow.AcceptedSuggestions);
                Assert.Equal($"{Client}-{Session}-Yeah", slow.AcceptedSuggestions[0]);

                Assert.Empty(fast.AcceptedSuggestions);
            }
            finally
            {
                SubsystemManager.UnregisterSubsystem <ICommandPredictor>(slow.Id);
                SubsystemManager.UnregisterSubsystem(SubsystemKind.CommandPredictor, fast.Id);
            }
        }
        static MyPredictor()
        {
            SlowPredictor = new MyPredictor(
                Guid.NewGuid(),
                "Test Predictor #1",
                "Description for #1 predictor.",
                delay: true);

            FastPredictor = new MyPredictor(
                Guid.NewGuid(),
                "Test Predictor #2",
                "Description for #2 predictor.",
                delay: false);
        }
 static SubsystemTests()
 {
     predictor1 = MyPredictor.FastPredictor;
     predictor2 = MyPredictor.SlowPredictor;
 }