Test_TaskExtensions.cs

// 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.VisualStudio.TestTools.UnitTesting;

namespace CommunityToolkit.Common.UnitTests.Extensions;

[TestClass]
public class Test_TaskExtensions
{
    [TestMethod]
    public void Test_TaskExtensions_NonGeneric_CompletedTask()
    {
        _ = Task.CompletedTask.GetResultOrDefault();
    }

    [TestMethod]
    public void Test_TaskExtensions_Generic_ValueType()
    {
        TaskCompletionSource<int> tcs = new();

        Assert.AreEqual(0, tcs.Task.GetResultOrDefault());

        tcs.SetResult(42);

        Assert.AreEqual(42, tcs.Task.GetResultOrDefault());
    }

    [TestMethod]
    public void Test_TaskExtensions_Generic_ReferenceType()
    {
        TaskCompletionSource<string?> tcs = new();

        Assert.AreEqual(null, tcs.Task.GetResultOrDefault());

        tcs.SetResult(nameof(Test_TaskExtensions_Generic_ReferenceType));

        Assert.AreEqual(nameof(Test_TaskExtensions_Generic_ReferenceType), tcs.Task.GetResultOrDefault());
    }

    [TestMethod]
    public void Test_TaskExtensions_ResultOrDefault()
    {
        TaskCompletionSource<int> tcs = new();

        Assert.AreEqual(null, ((Task)tcs.Task).GetResultOrDefault());

        tcs.SetCanceled();

        Assert.AreEqual(null, ((Task)tcs.Task).GetResultOrDefault());

        tcs = new TaskCompletionSource<int>();

        tcs.SetException(new InvalidOperationException("Test"));

        Assert.AreEqual(null, ((Task)tcs.Task).GetResultOrDefault());

        tcs = new TaskCompletionSource<int>();

        tcs.SetResult(42);

        Assert.AreEqual(42, ((Task)tcs.Task).GetResultOrDefault());
    }

    [TestMethod]
    public void Test_TaskExtensions_ResultOrDefault_FromTaskCompleted()
    {
        Assert.AreEqual(null, Task.CompletedTask.GetResultOrDefault());
    }

    [TestMethod]
    public async Task Test_TaskExtensions_ResultOrDefault_FromAsyncTaskMethodBuilder()
    {
        TaskCompletionSource<object?>? tcs = new();

        Task<string?> taskFromBuilder = GetTaskFromAsyncMethodBuilder("Test", tcs);

        Assert.IsNull(((Task)taskFromBuilder).GetResultOrDefault());
        Assert.IsNull(taskFromBuilder.GetResultOrDefault());

        tcs.SetResult(null);

        _ = await taskFromBuilder;

        Assert.AreEqual("Test", ((Task)taskFromBuilder).GetResultOrDefault());
        Assert.AreEqual("Test", taskFromBuilder.GetResultOrDefault());
    }

    [TestMethod]
    public void Test_TaskExtensions_ResultOrDefault_OfT_Int32()
    {
        TaskCompletionSource<int> tcs = new();

        Assert.AreEqual(0, tcs.Task.GetResultOrDefault());

        tcs.SetCanceled();

        Assert.AreEqual(0, tcs.Task.GetResultOrDefault());

        tcs = new TaskCompletionSource<int>();

        tcs.SetException(new InvalidOperationException("Test"));

        Assert.AreEqual(0, tcs.Task.GetResultOrDefault());

        tcs = new TaskCompletionSource<int>();

        tcs.SetResult(42);

        Assert.AreEqual(42, tcs.Task.GetResultOrDefault());
    }

    [TestMethod]
    public void Test_TaskExtensions_ResultOrDefault_OfT_String()
    {
        TaskCompletionSource<string?> tcs = new();

        Assert.AreEqual(null, tcs.Task.GetResultOrDefault());

        tcs.SetCanceled();

        Assert.AreEqual(null, tcs.Task.GetResultOrDefault());

        tcs = new TaskCompletionSource<string?>();

        tcs.SetException(new InvalidOperationException("Test"));

        Assert.AreEqual(null, tcs.Task.GetResultOrDefault());

        tcs = new TaskCompletionSource<string?>();

        tcs.SetResult("Hello world");

        Assert.AreEqual("Hello world", tcs.Task.GetResultOrDefault());
    }

    // Creates a Task<T> of a given type which is actually an instance of
    // System.Runtime.CompilerServices.AsyncTaskMethodBuilder<TResult>.AsyncStateMachineBox<TStateMachine>.
    // See https://source.dot.net/#System.Private.CoreLib/AsyncTaskMethodBuilderT.cs,f8f35fd356112b30.
    // This is needed to verify that the extension also works when the input Task<T> is of a derived type.
    private static async Task<T?> GetTaskFromAsyncMethodBuilder<T>(T? result, TaskCompletionSource<object?> tcs)
    {
        _ = await tcs.Task;

        return result;
    }
}