AutoMapperTests.cs

using AutoMapper;
using Xunit;

namespace AutomapperIssue.ReadOnly
{
    public class AutoMapperTests
    {
        [Fact]
        public void AutoMapperValueResolverSilentlyFailsToSetValueTest()
        {
            // Arrange
            var mapper = new MapperConfiguration(_ =>
                                                 {
                                                     _.CreateMap<Source, IDestination>()
                                                      .ForMember(d => d.ValueFromValueResolver, o => o.ResolveUsing<DestinationValueResolver>());

                                                     _.CreateMap<Source, IDestination>()
                                                      .As<Destination>();
                                                 }).CreateMapper();

            var source = new Source
                         {
                             Id = 42
                         };

            // Act
            var destination = mapper.Map<IDestination>(source);

            // Assert
            Assert.NotNull(destination.ValueFromValueResolver); // expecting destination.ValueFromValueResolver to be set via DestinationValueResolver
        }
    }

    public class Source
    {
        public int Id { get; set; }
    }

    public interface IDestination
    {
        string ValueFromValueResolver { get; }
    }

    public class Destination : IDestination
    {
        public string ValueFromValueResolver { get; set; }
    }

    public class DestinationValueResolver : IValueResolver<Source, IDestination, string>
    {
        public string Resolve(Source source,
                              IDestination destination,
                              string destMember,
                              ResolutionContext context)
        {
            return $"Value from source \"{source.Id}\".";
        }
    }
}