Nunit: Assert.Throws 不适用于异步委托

有了这个测试用例：

using System;
using System.Threading.Tasks;
using NUnit.Framework;

namespace NUnitAsync
{
    [TestFixture]
    public class Class1
    {
        [Test]
        public void MyAsyncThingTest()
        {
            var ioe = Assert.Throws<InvalidOperationException>(async () => await DelayedFailureAsync());
            Assert.That(ioe.Message, Is.EqualTo("ABC"));
        }

        [Test]
        public void MyAsyncThingFluentTest()
        {
            Assert.That(async () => await DelayedFailureAsync(), Throws.Exception.TypeOf<InvalidOperationException>().And.Message.EqualTo("ABC"));
        }

        static async Task DelayedFailureAsync()
        {
            await Task.Delay(TimeSpan.FromSeconds(2)).ConfigureAwait(false);
            throw new InvalidOperationException("ABC");
        }
    }
}

:negative_squared_cross_mark: MyAsyncThingTest失败并出现此异常：

Test Name:  MyAsyncThingTest
Test FullName:  NUnitAsync.Class1.MyAsyncThingTest
Test Source:    C:\Temp\NUnitAsync\NUnitAsync\Class1.cs : line 15
Test Outcome:   Failed
Test Duration:  0:00:00.004

Result StackTrace:  
at NUnit.Framework.Internal.AsyncInvocationRegion.Create(MethodInfo method)
   at NUnit.Framework.Assert.Throws(IResolveConstraint expression, TestDelegate code, String message, Object[] args)
   at NUnit.Framework.Assert.Throws[TActual](TestDelegate code, String message, Object[] args)
   at NUnit.Framework.Assert.Throws[TActual](TestDelegate code)
   at NUnitAsync.Class1.MyAsyncThingTest() in C:\Temp\NUnitAsync\NUnitAsync\Class1.cs:line 16
Result Message: System.ArgumentException : 'async void' methods are not supported, please use 'async Task' instead

:white_check_mark: MyAsyncThingFluentTest通过。

为什么会有差异？ Assert.Throws返回异常以进行进一步测试，这是Assert.That样式不提供的有用功能。