Test Hang Repro Project

packages.config

<?xml version="1.0" encoding="utf-8"?>
<packages>
  <package id="xunit.runner.console" version="2.4.0" />
  <package id="NUnit.ConsoleRunner" version="3.8.0" />
</packages>

run.sh

#!/usr/bin/env bash

nuget restore packages.config -PackagesDirectory ./packages
nuget restore TestHang.csproj

msbuild /v:q

mono ./packages/xunit.runner.console.2.4.0/tools/net462/xunit.console.exe ./bin/Debug/net462/TestHang.dll
mono ./packages/NUnit.ConsoleRunner.3.8.0/tools/nunit3-console.exe ./bin/Debug/net462/TestHang.dll

TestHang.csproj

<Project Sdk="Microsoft.NET.Sdk">

    <PropertyGroup>
        <TargetFramework>net462</TargetFramework>
    </PropertyGroup>

    <ItemGroup>
        <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.5.0" />
        <PackageReference Include="NUnit" Version="3.10.1" />
        <PackageReference Include="NUnit3TestAdapter" Version="3.10.0" />
        <PackageReference Include="RestSharp" Version="106.2.1" />
        <PackageReference Include="xunit" Version="2.3.1" />
        <PackageReference Include="xunit.runner.visualstudio" Version="2.3.1" />
    </ItemGroup>
</Project>

Tests.cs

using System.Collections.Generic;
using NUnit.Framework;
using RestSharp;
using Xunit;

namespace TestHang
{
    public class XunitTest
    {
        [Fact]
        public void Xunit_Execute_WhenRequestIsPost_DoesNotHang()
        {
            var client = new RestClient("https://httpbin.org/");

            var request = new RestRequest("post", Method.POST);
            request.AddJsonBody(
                new Dictionary<string, string>
                {
                    { "hello", "world" },
                }
            );

            client.Execute(request);
        }
    }

    public class NUnitTest
    {
        [Test]
        public void NUnit_Execute_WhenRequestIsPost_DoesNotHang()
        {
            var client = new RestClient("https://httpbin.org/");

            var request = new RestRequest("post", Method.POST);
            request.AddJsonBody(
                new Dictionary<string, string>
                {
                    { "hello", "world" },
                }
            );

            client.Execute(request);
        }
    }
}