AsyncShouldlyTest.cs

using System;
using System.Threading.Tasks;
using Shouldly;
using Xunit;

namespace ClassLibrary9
{
    public class Sample
    {

        public async Task DoSomething()
        {
            throw new Exception("test");
        }
    }

    public class TestFixture
    {
        [Fact]
        public void ShouldThrow()
        {
            var sample = new Sample();

            var exception = Should.ThrowAsync<Exception>(() => sample.DoSomething());
        }
    }