[browser] test that Task.Yield yields to browser event loop (#113531)

Author: pavelsavara

src/libraries/System.Runtime.InteropServices.JavaScript/tests/System.Runtime.InteropServices.JavaScript.UnitTests/System.Runtime.InteropServices.JavaScript.Tests.csproj

@@ -32,6 +32,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\InteropServices\JavaScript\JavaScriptTestHelper.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\InteropServices\JavaScript\JSImportTest.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\InteropServices\JavaScript\JSExportTest.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\InteropServices\JavaScript\YieldAwaitableTests.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\InteropServices\JavaScript\JSInteropTestBase.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\InteropServices\JavaScript\Utils.cs" />
 

src/libraries/System.Runtime.InteropServices.JavaScript/tests/System.Runtime.InteropServices.JavaScript.UnitTests/System/Runtime/InteropServices/JavaScript/JavaScriptTestHelper.cs

@@ -1032,6 +1032,15 @@ public static JSObject EchoIJSObject([JSMarshalAs<JSType.Object>] JSObject arg1)
             return arg1;
         }
 
+        [JSImport("beforeYield", "JavaScriptTestHelper")]
+        public static partial void BeforeYield();
+
+        [JSImport("isSetTimeoutHit", "JavaScriptTestHelper")]
+        public static partial bool IsSetTimeoutHit();
+
+        [JSImport("isPromiseThenHit", "JavaScriptTestHelper")]
+        public static partial bool IsPromiseThenHit();
+
         [JSImport("callJavaScriptLibrary", "JavaScriptTestHelper")]
         public static partial Task<int> callJavaScriptLibrary(int a, int b);
 

src/libraries/System.Runtime.InteropServices.JavaScript/tests/System.Runtime.InteropServices.JavaScript.UnitTests/System/Runtime/InteropServices/JavaScript/JavaScriptTestHelper.mjs

@@ -466,3 +466,28 @@ export function delay(ms) {
 export function reject(what) {
     return new Promise((_, reject) => globalThis.setTimeout(() => reject(what), 0));
 }
+
+let setTimeoutHit = false;
+let promiseThenHit = false;
+export function beforeYield() {
+    setTimeoutHit = false;
+    promiseThenHit = false;
+    setTimeout(() => {
+        setTimeoutHit = true;
+    }, 0);
+    let res;
+    new Promise((resolve) => {
+        res = resolve;
+    }).then(() => {
+        promiseThenHit = true;
+    });
+    res();
+}
+
+export function isSetTimeoutHit() {
+    return setTimeoutHit;
+}
+
+export function isPromiseThenHit() {
+    return promiseThenHit;
+}

src/libraries/System.Runtime.InteropServices.JavaScript/tests/System.Runtime.InteropServices.JavaScript.UnitTests/System/Runtime/InteropServices/JavaScript/YieldAwaitableTests.cs

@@ -0,0 +1,54 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Xunit;
+using System;
+using System.Collections.Generic;
+using System.Runtime.CompilerServices;
+using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace System.Runtime.InteropServices.JavaScript.Tests
+{
+    public class YieldAwaitableTests : IAsyncLifetime
+    {
+        [Fact]
+        public async Task TaskYieldsToBrowserLoop()
+        {
+            JavaScriptTestHelper.BeforeYield();
+            await Task.Yield();
+            Assert.True(JavaScriptTestHelper.IsSetTimeoutHit());
+            Assert.True(JavaScriptTestHelper.IsPromiseThenHit());
+        }
+
+        [Fact]
+        public async Task TaskDelay0DoesNotYieldToBrowserLoop()
+        {
+            JavaScriptTestHelper.BeforeYield();
+            await Task.Delay(0);
+            Assert.False(JavaScriptTestHelper.IsSetTimeoutHit());
+            Assert.False(JavaScriptTestHelper.IsPromiseThenHit());
+        }
+
+        [Fact]
+        public async Task TaskDelay1YieldsToBrowserLoop()
+        {
+            JavaScriptTestHelper.BeforeYield();
+            await Task.Delay(1);
+            Assert.True(JavaScriptTestHelper.IsSetTimeoutHit());
+            Assert.True(JavaScriptTestHelper.IsPromiseThenHit());
+        }
+
+        public async Task InitializeAsync()
+        {
+            await JavaScriptTestHelper.InitializeAsync();
+            await Task.Delay(100);
+        }
+
+        public async Task DisposeAsync()
+        {
+            await JavaScriptTestHelper.DisposeAsync();
+        }
+    }
+}