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POUnit testing for an event using Reactive Extensions
 

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    <p>I'm using <a href="http://msdn.microsoft.com/en-us/devlabs/ee794896.aspx" rel="noreferrer">Reactive Extensions for .NET (Rx)</a> to expose events as <code>IObservable&lt;T&gt;</code>. I want to create an unit test where I assert that a particular event is fired. Here is a simplified version of the class I want to test:</p> <pre><code>public sealed class ClassUnderTest : IDisposable { Subject&lt;Unit&gt; subject = new Subject&lt;Unit&gt;(); public IObservable&lt;Unit&gt; SomethingHappened { get { return this.subject.AsObservable(); } } public void DoSomething() { this.subject.OnNext(new Unit()); } public void Dispose() { this.subject.OnCompleted(); } } </code></pre> <p>Obviously my real classes are more complex. My goal is to verify that performing some actions with the class under test leads to a sequence of events signaled on the <code>IObservable</code>. Luckily the classes I want to test implement <code>IDisposable</code> and calling <code>OnCompleted</code> on the subject when the object is disposed makes it much easier to test.</p> <p>Here is how I test:</p> <pre><code>// Arrange var classUnderTest = new ClassUnderTest(); var eventFired = false; classUnderTest.SomethingHappened.Subscribe(_ =&gt; eventFired = true); // Act classUnderTest.DoSomething(); // Assert Assert.IsTrue(eventFired); </code></pre> <p>Using a variable to determine if an event is fired isn't too bad, but in more complex scenarios I may want to verify that a particular sequence of events are fired. Is that possible without simply recording the events in variables and then doing assertions on the variables? Being able to use a fluent LINQ-like syntax to make assertions on an <code>IObservable</code> would hopefully make the test more readable.</p>
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    1. USMartin Liversage
    1. USMartin Liversage
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    1. COBTW, I think having a variable is perfectly good. The code above is easy to read, which is most important. The @PL's answer is nice and elegant, but you have to strain to understand what is going on... Maybe transform it to an extension FailIfNothingHappened()
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      1. USSergey Aldoukhov
    2. CO@Sergey Aldoukhov: I agree, but PL's answer learned me how I can use `Materialize` to reason about how my `IObservable` behaves. And for more complex tests using variables to capture what happened may be harder to understand. Also, creating an extension as you suggest will probably make it easier to understand what is going on.
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      1. USMartin Liversage
    3. COI have edited my question to make it more clear what I want.
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