Added tests for the TaskExtensions class

UnitTests/Extensions/Test_TaskExtensions.cs

@@ -0,0 +1,51 @@
+// 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.Threading.Tasks;
+using Microsoft.Toolkit.Extensions;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace UnitTests.Extensions
+{
+    [TestClass]
+    public class Test_TaskExtensions
+    {
+        [TestCategory("TaskExtensions")]
+        [TestMethod]
+        public void Test_TaskExtensions_Nongeneric()
+        {
+#pragma warning disable CS0618 // Type or member is obsolete
+            Assert.ThrowsException<NotImplementedException>(() => default(Task).ResultOrDefault());
+            Assert.ThrowsException<NotImplementedException>(() => Task.CompletedTask.ResultOrDefault());
+#pragma warning restore CS0618
+        }
+
+        [TestCategory("TaskExtensions")]
+        [TestMethod]
+        public void Test_TaskExtensions_Generic_ValueType()
+        {
+            TaskCompletionSource<int> tcs = new TaskCompletionSource<int>();
+
+            Assert.AreEqual(0, tcs.Task.ResultOrDefault());
+
+            tcs.SetResult(42);
+
+            Assert.AreEqual(42, tcs.Task.ResultOrDefault());
+        }
+
+        [TestCategory("TaskExtensions")]
+        [TestMethod]
+        public void Test_TaskExtensions_Generic_ReferenceType()
+        {
+            TaskCompletionSource<string> tcs = new TaskCompletionSource<string>();
+
+            Assert.AreEqual(null, tcs.Task.ResultOrDefault());
+
+            tcs.SetResult(nameof(Test_TaskExtensions_Generic_ReferenceType));
+
+            Assert.AreEqual(nameof(Test_TaskExtensions_Generic_ReferenceType), tcs.Task.ResultOrDefault());
+        }
+    }
+}