<PackageReference Include="NUnit" Version="4.2.2" />

ICallbackEventHandler

public interface ICallbackEventHandler
A shim of the .NET interface for platforms that do not support it. Used to indicate that a control can be the target of a callback event on the server.
using System.Runtime.CompilerServices; namespace System.Web.UI { [System.Runtime.CompilerServices.NullableContext(1)] public interface ICallbackEventHandler { void RaiseCallbackEvent(string report); string GetCallbackResult(); } }