NSubstitute and Async

Test Async

using System.Threading.Tasks;
using NSubstitute;
using NUnit.Framework;

namespace ClassLibrary1
{
    public interface ICalculationServiceAsync
    {
        Task Calculate();
    }

    public class SystemUnderTest
    {
        private readonly ICalculationServiceAsync _service;

        public SystemUnderTest(ICalculationServiceAsync service)
        {
            _service = service;
        }

        public async void DoSomethingAsync()
        {
            await _service.Calculate();
        }
    }

    [TestFixture]
    public class AsyncTest
    {
        [Test]
        public void Can_await_on_async_mocks()
        {
            var mockService = Substitute.For<ICalculationServiceAsync>();
            var sut = new SystemUnderTest(mockService);

            sut.DoSomethingAsync();

            mockService.Calculate().ReceivedCalls();
        }
    }
}