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Tamir Dresher (@tamir_dresher)
Senior Software ArchitectJ
Testing Time and Concurrency with Rx
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• Author of Rx.NET in Action (manning publications)
• Software architect, consultant and instructor
• Software Engineering Lecturer @ Ruppin Academic Center
• OzCode (www.oz-code.com) Evangelist
@[email protected]://www.TamirDresher.com.
About Me
Reactive Extensions (Rx)
Your headache relief pill to Asynchronous Event
based applications
AsyncPush
Triggers
Events
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Reacting to changes
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IEnumerable<Message> LoadMessages(string hashtag)
{
var statuses = facebook.Search(hashtag);
var tweets = twitter.Search(hashtag);
var updates = linkedin.Search(hashtag);
return statuses.Concat(tweets).Concat(updates);
}
Twitter App
Pull ModelPull Model
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???? LoadMessages(string hashtag)
{
facebook.Search(hashtag);
twitter.Search(hashtag);
linkedin.Search(hashtag);
}
DoSomething( )msg
Push ModelPush Model
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namespace System{
public interface IObservable<out T>{
IDisposable Subscribe(IObserver<T> observer);}
public interface IObserver<in T>{
void OnNext(T value);void OnError(Exception error);void OnCompleted();
}}
InterfacesInterfaces
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observable observer
Subscribe(observer)
subscription
OnNext(X1)
OnNext(Xn)⁞
⁞
IDisposable
Observables and ObserversObservables and Observers
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OnCompleted()
OnError(Exception)
observable observer
⁞
Observables and ObserversObservables and Observers
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Rx packages
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Push ModelPush Model with Rx Observables
class ReactiveSocialNetworksManager{
//members
public IObservable<Message> ObserveMessages(string hashtag){
:}
}
var mgr = new ReactiveSocialNetworksManager();
mgr.ObserveMessages("Rx").Subscribe(
msg => Console.WriteLine($"Observed:{msg} \t"),ex => { /*OnError*/ },() => { /*OnCompleted*/ });
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Creating Observables
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Observable.Range(1, 10)
.Subscribe(x => Console.WriteLine(x));
Observable.Interval(TimeSpan.FromSeconds(1)).Subscribe(x => Console.WriteLine(x));
Observable.FromEventPattern(SearchBox, "TextChanged")
⁞
⁞1 sec 1 sec
Observables Factories
⁞
Observables Factories
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Observable Queries (Rx Operators)
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Filtering Projection Partitioning Joins Grouping Set
Element Generation Quantifiers Aggregation Error HandlingTime and Concurrency
Where
OfType
Select
SelectMany
Materialize
Skip
Take
TakeUntil
CombineLatest
Concat
join
GroupBy
GroupByUntil
Buffer
Distinct
DistinctUntilChanged
Timeout
TimeInterval
ElementAt
First
Single
Range
Repeat
Defer
All
Any
Contains
Sum
Average
Scan
Catch
OnErrorResumeNext
Using
Rx operators
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Reactive SearchReactive Search
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1. At least 3 characters2. Don’t overflow server (0.5 sec delay)3. Don’t send the same string again4. Discard results if another search was requested
Reactive Search - RulesReactive Search - Rules
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Where(s => s.Length > 2 )
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Where(s => s.Length > 2 )
Throttle(TimeSpan.FromSeconds(0.5))
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Where(s => s.Length > 2 )
Throttle(TimeSpan.FromSeconds(0.5))
DistinctUntilChanged()
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Select(text => SearchAsync(text))
“REA”
“REAC”
Switch()
“REA” results are ignored since we switched to the “REAC” results
Abstracting Time and Concurrency
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Thread Pool
Task Scheduler
other
SchedulersSchedulers
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public interface IScheduler{
DateTimeOffset Now { get; }
IDisposable Schedule<TState>( TState state, Func<IScheduler, TState, IDisposable> action);
IDisposable Schedule<TState>(TimeSpan dueTime, TState state,Func<IScheduler, TState, IDisposable> action);
IDisposable Schedule<TState>(DateTimeOffset dueTime, TState state,Func<IScheduler, TState, IDisposable> action);
}
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//// Runs a timer on the default scheduler//IObservable TimeSpan
//// Every operator that introduces concurrency// has an overload with an IScheduler//IObservable T TimeSpan
IScheduler scheduler);
Parameterizing ConcurrencyParameterizing Concurrency
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textChanged.Throttle(TimeSpan.FromSeconds(0.5),
DefaultScheduler.Instance).DistinctUntilChanged().SelectMany(text => SearchAsync(text)).Switch().Subscribe(/*handle the results*/);
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//// runs the observer callbacks on the specified // scheduler.//IObservable T ObserveOn<T>(IScheduler);
//// runs the observer subscription and unsubsciption on// the specified scheduler.//IObservable T SubscribeOn<T>(IScheduler)
Changing Execution ContextChanging Execution Context
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textChanged.Throttle(TimeSpan.FromSeconds(0.5)).DistinctUntilChanged().Select(text => SearchAsync(text)).Switch().ObserveOn(DispatcherScheduler.Current).Subscribe(/*handle the results*/);
Changing Execution ContextChanging Execution Context
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textChanged.Throttle(TimeSpan.FromSeconds(0.5)).DistinctUntilChanged().Select(text => SearchAsync(text)).Switch().ObserveOnDispatcher().Subscribe(/*handle the results*/);
Changing Execution ContextChanging Execution Context
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Virtual Time
What is time?
Time can be a anything that is sequential and comparable
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“Time is the indefinite continued progress of existence and events ... Time
is a component quantity of various measurements used
to sequence events, to compare the duration of events or the intervals
between them…”
https://en.wikipedia.org/wiki/Time
Virtual Time Scheduler
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public abstract class VirtualTimeSchedulerBase<TAbsolute, TRelative> : IScheduler,
IServiceProvider, IStopwatchProvider
where TAbsolute : IComparable<TAbsolute>
{
public TAbsolute Clock { get; protected set;}
public void Start()
public void Stop()
public void AdvanceTo(TAbsolute time)
public void AdvanceBy(TRelative time)
...
}
public class TestScheduler : VirtualTimeScheduler<long, long>{
...}
Testing Rx
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1. At least 3 characters One letter word, No Search performed
2. Don’t overflow server (0.5 sec delay) 2 words typed, 0.2 sec gap, search only the last
3. Don’t send the same string again 2 words, 1 sec gap, same value, search only first
4. Discard results if another search was requested 2 words, 1 sec gap, slow first search, fast last search, last results shown
Reactive Search - RulesReactive Search – Rules Tests
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Questions and Answers
Q: How can we test the code without a real user interaction?
Q: How can we test the code without a real server?
Q: How can we test the code deterministically without a real asynchronicity and concurrency?
Q: How can we test the code without REALLY waiting for the time to pass?
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A: Separation of concerns. Separate the logic from the view
A: Enable Dependency Injection and mock the service client
A: Leverage the Rx Schedulers and provide a Scheduler you can control via DI
A: Leverage the Rx TestScheduler which provides a virtualization of time
Separating the logic from the view
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SearchView(Presentation, Logic, State)
SearchView(Presentation)
SearchViewModel(Logic, State)
Before
After
Separating the logic from the view
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<Window x:Class="TestableReactiveSearch.SearchView"><DockPanel>
<TextBox x:Name="SearchBox"Text="{Binding SearchTerm …}"DockPanel.Dock="Top“/>
<ListBox x:Name="SearchResults"ItemsSource="{Binding SearchResults}“/>
</DockPanel></Window>
public class SearchViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public SearchViewModel()
{
// Rx query
}
public string SearchTerm { get { ... } set { ... } }
public IEnumerable<string> SearchResults { get { ... } set { ... } }}
SearchView.xaml
SearchViewModel.cs
Separating the logic from the view – fixing the Rx query
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public SearchViewModel()
{
var terms =
Observable.FromEventPattern<PropertyChangedEventArgs>(this, nameof(PropertyChanged))
.Where(e => e.EventArgs.PropertyName == nameof(SearchTerm))
.Select(_ => SearchTerm);
_subscription =
terms
.Where(txt => txt.Length >= 3)
.Throttle(TimeSpan.FromSeconds(0.5))
.DistinctUntilChanged()
.Select(txt => searchServiceClient.SearchAsync(txt))
.Switch()
.ObserveOnDispatcher()
.Subscribe(
results => SearchResults = results,
err => { Debug.WriteLine(err); },
() => { /* OnCompleted */ });
}
Same query as before
Injecting the Search Service client
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public class SearchViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public SearchViewModel()
{
// rest of rx query
}
...}
Injecting the Search Service client
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public class SearchViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public SearchViewModel(ISearchServiceClient searchServiceClient)
{
// rest of rx query
}
...}
Simple test – first try
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[TestMethod]
public void Search_OneLetterWord_NoSearchSentToService()
{
var fakeServiceClient = Substitute.For<ISearchServiceClient>();
var vm = new SearchViewModel(fakeServiceClient);
vm.SearchTerm = "A";
fakeServiceClient.DidNotReceive().SearchAsync("A");
}
Injecting concurrency
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public interface IConcurrencyProvider{
IScheduler TimeBasedOperations { get; }IScheduler Task { get; }IScheduler Thread { get; }IScheduler Dispatcher { get; }
}class ConcurrencyProvider : IConcurrencyProvider{
public ConcurrencyProvider(){
TimeBasedOperations = DefaultScheduler.Instance;Task = TaskPoolScheduler.Default;Thread = NewThreadScheduler.Default;Dispatcher=DispatcherScheduler.Current;
}
public IScheduler TimeBasedOperations { get; }public IScheduler Task { get; }public IScheduler Thread { get; }public IScheduler Dispatcher { get; }
}
Injecting concurrency
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public SearchViewModel(ISearchServiceClient searchServiceClient,
IConcurrencyProvider concurrencyProvider)
{
var terms =
Observable.FromEventPattern<PropertyChangedEventArgs>(this, nameof(PropertyChanged))
.Where(e => e.EventArgs.PropertyName == nameof(SearchTerm)).Select(_=>SearchTerm);
_subscription =
terms
.Where(txt => txt.Length >= 3)
.Throttle(TimeSpan.FromSeconds(0.5), concurrencyProvider.Thread)
.DistinctUntilChanged()
.Select(txt => searchServiceClient.SearchAsync(txt))
.Switch()
.ObserveOn(concurrencyProvider.Dispatcher)
.Subscribe(
results => SearchResults = results,
err => { Debug.WriteLine(err); },
() => { /* OnCompleted */ });
}
Simplest Rx Test
Install-Package Microsoft.Reactive.Testing
To simplify the Rx testing, derive your test class from ReactiveTest
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using Microsoft.Reactive.Testing;
[TestClass]
public class SearchViewModelTests : ReactiveTest
{
// Test Methods
}
Test 1: Search is sent after half a sec
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const long ONE_SECOND = TimeSpan.TicksPerSecond;
[TestMethod]
public void MoreThanThreeLetters_HalfSecondGap_SearchSentToService()
{
var fakeServiceClient = Substitute.For<ISearchServiceClient>();
var fakeConcurrencyProvider = Substitute.For<IConcurrencyProvider>();
var testScheduler = new TestScheduler();
fakeConcurrencyProvider.ReturnsForAll<IScheduler>(testScheduler);
var vm = new SearchViewModel(fakeServiceClient, fakeConcurrencyProvider);
testScheduler.Start();
vm.SearchTerm = "reactive";
testScheduler.AdvanceBy(ONE_SECOND / 2);
fakeServiceClient.Received().SearchAsync("reactive");
}
TestScheduler
TestScheduler provides two methods for creating observables:CreateColdObservable – Creates an observable that emits its value relatively to when each observer subscribes.
CreateHotObservable – Creates and observable that emits its values regardless to the observer subscription time, and each emission is configured to the absolute scheduler clock
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var testScheduler = new TestScheduler();
ITestableObservable<int> coldObservable = testScheduler.CreateColdObservable<int>(OnNext<int>(20, 1),OnNext<int>(40, 2),OnCompleted<int>(60)
);
Test 2: first search is discarded if another search happens
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public void TwoValidWords_SlowSearchThenFastSearch_SecondSearchResultsOnly()
{
var fakeServiceClient = Substitute.For<ISearchServiceClient>();
var fakeConcurrencyProvider = Substitute.For<IConcurrencyProvider>();
var testScheduler = new TestScheduler();
fakeConcurrencyProvider.ReturnsForAll<IScheduler>(testScheduler);
fakeServiceClient.SearchAsync("first").Returns(testScheduler.CreateColdObservable(
OnNext<IEnumerable<string>>(2 * ONE_SECOND, new[] {"first"}), ...);
fakeServiceClient.SearchAsync("second").Returns(testScheduler.CreateColdObservable(
OnNext<IEnumerable<string>>(1, new[] { "second" }), ...);
var vm = new SearchViewModel(fakeServiceClient, fakeConcurrencyProvider);
testScheduler.Start();
vm.SearchTerm = "first";
testScheduler.AdvanceBy(ONE_SECOND);
vm.SearchTerm = "second";
testScheduler.AdvanceBy(5 * ONE_SECOND);
Assert.AreEqual("second", vm.SearchResults.First());
}
Summary
Pull vs. Push model
Rx operators
Building Rx queries
Rx Concurrency Model
Virtual Time
Testing Time and Concurrency with TestScheduler
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Your headache relief pill to Asynchronous and
Event based applications
AsyncPush
Triggers
Events
Reactive ExtensionsReactive Extensions
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www.reactivex.io github.com/Reactive-Extensionswww.manning.com/dresher
Thank You
Tamir Dresher (@tamir_dresher)
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