ContinuationTests.cs

using Microsoft.VisualStudio.TestTools.UnitTesting;
using System.Threading.Tasks;

namespace FuncContravarianceIssue
{
    [TestClass]
    public class UnitTest1
    {
        private class Foo
        {

        }

        [TestMethod]
        public async Task TestMethod1()
        {
            var data = new Foo();
            Task continuationCallback(Task input, Foo state)
            {
                return Task.CompletedTask;
            }

            await Task.Delay(1).ContinueWith<Task>(
                continuationFunction: continuationCallback, 
                state: data);
        }
    }
}