Add unit tests for messenger observable APIs

tests/CommunityToolkit.Mvvm.Roslyn401.UnitTests/CommunityToolkit.Mvvm.Roslyn401.UnitTests.csproj

@@ -9,6 +9,7 @@
     <PackageReference Include="MSTest.TestAdapter" Version="2.2.8" />
     <PackageReference Include="MSTest.TestFramework" Version="2.2.8" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.0.0" />
+    <PackageReference Include="System.Reactive" Version="5.0.0" />
     <PackageReference Include="System.Text.Json" Version="6.0.6" />
   </ItemGroup>
 

tests/CommunityToolkit.Mvvm.Roslyn430.UnitTests/CommunityToolkit.Mvvm.Roslyn430.UnitTests.csproj

@@ -9,6 +9,7 @@
     <PackageReference Include="MSTest.TestAdapter" Version="2.2.8" />
     <PackageReference Include="MSTest.TestFramework" Version="2.2.8" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.0.0" />
+    <PackageReference Include="System.Reactive" Version="5.0.0" />
     <PackageReference Include="System.Text.Json" Version="6.0.6" />
   </ItemGroup>
 

tests/CommunityToolkit.Mvvm.UnitTests/CommunityToolkit.Mvvm.UnitTests.projitems

@@ -25,6 +25,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Test_AsyncRelayCommand{T}.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Test_INotifyPropertyChangedAttribute.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Test_IRecipientGenerator.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Test_Messenger.Observables.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Test_Messenger.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Test_Messenger.Request.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Test_ObservableObject.cs" />

tests/CommunityToolkit.Mvvm.UnitTests/Test_Messenger.Observables.cs

@@ -0,0 +1,102 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Collections.Generic;
+using CommunityToolkit.Mvvm.Messaging;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace CommunityToolkit.Mvvm.UnitTests;
+
+partial class Test_Messenger
+{
+    [TestMethod]
+    [DataRow(typeof(StrongReferenceMessenger))]
+    [DataRow(typeof(WeakReferenceMessenger))]
+    public void Test_Messenger_CreateObservable(Type type)
+    {
+        IMessenger messenger = (IMessenger)Activator.CreateInstance(type)!;
+
+        IObservable<MessageA> observable = messenger.CreateObservable<MessageA>();
+
+        Assert.IsNotNull(observable);
+
+        List<MessageA> messages = new();
+
+        IDisposable disposable = observable.Subscribe(messages.Add);
+
+        MessageA message1 = new();
+        MessageA message2 = new();
+
+        _ = messenger.Send(message1);
+        _ = messenger.Send(message2);
+
+        // The expected messages have been observed
+        CollectionAssert.AreEqual(messages, new[] { message1, message2 });
+
+        disposable.Dispose();
+
+        _ = messenger.Send<MessageA>();
+
+        // No messages are sent after unsubscribing the observable
+        CollectionAssert.AreEqual(messages, new[] { message1, message2 });
+    }
+
+    [TestMethod]
+    [DataRow(typeof(StrongReferenceMessenger))]
+    [DataRow(typeof(WeakReferenceMessenger))]
+    public void Test_Messenger_CreateObservable_WithToken(Type type)
+    {
+        IMessenger messenger = (IMessenger)Activator.CreateInstance(type)!;
+
+        IObservable<MessageA> observable = messenger.CreateObservable<MessageA, int>(42);
+
+        Assert.IsNotNull(observable);
+
+        List<MessageA> messages = new();
+
+        IDisposable disposable = observable.Subscribe(messages.Add);
+
+        MessageA message1 = new();
+        MessageA message2 = new();
+
+        _ = messenger.Send(message1, 42);
+        _ = messenger.Send(message2, 42);
+
+        _ = messenger.Send(new MessageA(), 1);
+        _ = messenger.Send(new MessageA(), 999);
+
+        // The expected messages have been observed (only for matching tokens)
+        CollectionAssert.AreEqual(messages, new[] { message1, message2 });
+
+        disposable.Dispose();
+
+        _ = messenger.Send(new MessageA(), 42);
+        _ = messenger.Send(new MessageA(), 1);
+
+        // No messages are sent after unsubscribing the observable (regardless of token)
+        CollectionAssert.AreEqual(messages, new[] { message1, message2 });
+    }
+
+    [TestMethod]
+    [ExpectedException(typeof(ArgumentNullException))]
+    public void Test_Messenger_CreateObservable_NullMessenger()
+    {
+        _ = IMessengerExtensions.CreateObservable<MessageA>(null!);
+    }
+
+    [TestMethod]
+    [ExpectedException(typeof(ArgumentNullException))]
+    public void Test_Messenger_CreateObservable_WithToken_NullMessenger()
+    {
+        _ = IMessengerExtensions.CreateObservable<MessageA, string>(null!, "Hello");
+    }
+
+    [TestMethod]
+    [ExpectedException(typeof(ArgumentNullException))]
+    public void Test_Messenger_CreateObservable_WithToken_NullToken()
+    {
+        _ = IMessengerExtensions.CreateObservable<MessageA, string>(new WeakReferenceMessenger(), null!);
+    }
+}

tests/CommunityToolkit.Mvvm.UnitTests/Test_Messenger.Request.cs

@@ -12,7 +12,7 @@
 
 namespace CommunityToolkit.Mvvm.UnitTests;
 
-public partial class Test_Messenger
+partial class Test_Messenger
 {
     [TestMethod]
     [DataRow(typeof(StrongReferenceMessenger))]