如何在单元测试中验证Flurl Http中的请求正文内容？

Question

我正在使用Flurl Http发出http请求。在单元测试中，我试图验证预期的内容是否已传递给发件人。我正在尝试：

httpTest.ShouldHaveCalled(url)
        .WithVerb(HttpMethod.Post)
        .WithContentType(contentType)
        .With(w => w.Request.Content.ReadAsStringAsync().Result == content)
        .Times(1);

但是，此操作失败，并显示System.ObjectDisposedException Cannot access a disposed object. Object name: 'System.Net.Http.StringContent'.

看起来Flurl在测试中完成验证之前正在处理请求正文内容。如何捕获请求正文以进行验证？

编辑（完全可复制的示例）：

using System;
using System.Net.Http;
using System.Text;
using System.Threading.Tasks;

using Autofac.Extras.Moq;

using Flurl.Http;
using Flurl.Http.Testing;

using Xunit;

namespace XUnitTestProject1
{
    public class MyClassTest : IDisposable
    {
        private readonly AutoMock container;
        private readonly HttpTest client;

        public MyClassTest()
        {
            this.container = AutoMock.GetLoose();
            this.client = new HttpTest();
        }

        [Fact]
        public async Task SendAsync_ValidateRequestBody()
        {
            const string url = "http://www.example.com";
            const string content = "Hello, world";

            var sut = this.container.Create<MyClass>();
            await sut.SendAsync(url, content);

            this.client.ShouldHaveCalled(url)
                .With(w =>
                      {
                          var x = w.RequestBody;
                          return w.RequestBody == content;
                      });
        }

        public void Dispose()
        {
            this.container?.Dispose();
            this.client?.Dispose();
        }
    }

    public class MyClass
    {
        public virtual async Task SendAsync(string url, string content)
        {
            await url.PostAsync(new StringContent(content, Encoding.UTF8, "text/plain"));
        }
    }
}