Fix RxSchedulers not being set by ReactiveUI.Testing SchedulerExtensions (#4184)

Author: Cheesebaron

src/ReactiveUI.Testing.Tests/SchedulerExtensionTests.cs

@@ -0,0 +1,54 @@
+// Copyright (c) 2025 .NET Foundation and Contributors. All rights reserved.
+// 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 full license information.
+
+using System.Collections.Generic;
+using Microsoft.Reactive.Testing;
+using NUnit.Framework;
+
+namespace ReactiveUI.Testing.Tests;
+
+/// <summary>
+/// Tests for <see cref="SchedulerExtensions"/>.
+/// </summary>
+[TestFixture]
+public sealed class SchedulerExtensionTests
+{
+    /// <summary>
+    /// Tests that WithScheduler sets both RxApp and RxSchedulers schedulers.
+    /// </summary>
+    [Test]
+    public void WithScheduler_ShouldSetBothRxAppAndRxSchedulersSchedulers()
+    {
+        var testScheduler = new TestScheduler();
+        var originalMainThread = RxApp.MainThreadScheduler;
+        var originalTaskpool = RxApp.TaskpoolScheduler;
+        var originalRxSchedulersMain = RxSchedulers.MainThreadScheduler;
+        var originalRxSchedulersTask = RxSchedulers.TaskpoolScheduler;
+
+        using (SchedulerExtensions.WithScheduler(testScheduler))
+        {
+            // Verify schedulers
+            using (Assert.EnterMultipleScope())
+            {
+                // Verify RxApp schedulers are set
+                Assert.That(RxApp.MainThreadScheduler, Is.EqualTo(testScheduler));
+                Assert.That(RxApp.TaskpoolScheduler, Is.EqualTo(testScheduler));
+
+                // Verify RxSchedulers are set
+                Assert.That(RxSchedulers.MainThreadScheduler, Is.EqualTo(testScheduler));
+                Assert.That(RxSchedulers.TaskpoolScheduler, Is.EqualTo(testScheduler));
+            }
+        }
+
+        // Verify schedulers are restored after disposal
+        using (Assert.EnterMultipleScope())
+        {
+            Assert.That(RxApp.MainThreadScheduler, Is.EqualTo(originalMainThread));
+            Assert.That(RxApp.TaskpoolScheduler, Is.EqualTo(originalTaskpool));
+            Assert.That(RxSchedulers.MainThreadScheduler, Is.EqualTo(originalRxSchedulersMain));
+            Assert.That(RxSchedulers.TaskpoolScheduler, Is.EqualTo(originalRxSchedulersTask));
+        }
+    }
+}

src/ReactiveUI.Testing/SchedulerExtensions.cs

@@ -32,14 +32,20 @@ public static IDisposable WithScheduler(IScheduler scheduler)
         _schedulerGate.WaitOne();
         var prevDef = RxApp.MainThreadScheduler;
         var prevTask = RxApp.TaskpoolScheduler;
+        var prevRxDef = RxSchedulers.MainThreadScheduler;
+        var prevRxTask = RxSchedulers.TaskpoolScheduler;
 
         RxApp.MainThreadScheduler = scheduler;
         RxApp.TaskpoolScheduler = scheduler;
+        RxSchedulers.MainThreadScheduler = scheduler;
+        RxSchedulers.TaskpoolScheduler = scheduler;
 
         return Disposable.Create(() =>
         {
             RxApp.MainThreadScheduler = prevDef;
             RxApp.TaskpoolScheduler = prevTask;
+            RxSchedulers.MainThreadScheduler = prevRxDef;
+            RxSchedulers.TaskpoolScheduler = prevRxTask;
             _schedulerGate.Set();
         });
     }