Mapping Test errors when using Value Resolvers with dependencies

[DMEvans]

When attempting to verify the supported mappings via ShouldSupportMappingFromSourceToDestination an error will occur if any of your mappers use a ValueResolver which doesn't include an empty constructor.

An example of when this occurred for me was when attempting to map a request object containing an IEnumerable to a SQL parameters object containing a DataTable to facilitate passing the values via Dapper as TVP. I have service which handles the conversion which is injected into a ValueResolver, since services cannot be injected into the Profile class.

public class DataTableResolver<TSource, TDestination> : IValueResolver<TSource, TDestination, DataTable>
{
    private readonly IDataTableUtility _dataTableUtility;

    public DataTableResolver(IDataTableUtility dataTableUtility)
    {
        _dataTableUtility = dataTableUtility;
    }

    public DataTable Resolve(TSource source, TDestination destination, DataTable destMember, ResolutionContext context)
    {
        // ... do stuff with IDataTableUtility to return a DataTable
    }
}

Because the mapper is created directly from the configuration the dependency injection cannot be resolved.

public MappingTests()
{
    _configuration = new MapperConfiguration(config => config.AddProfile<MappingProfile>());

    _mapper = _configuration.CreateMapper();
}

In order to resolve this in my own project I modified the test constructor to use an IServiceProvider to instantiate the mapper, which allowed me to include the relevant dependencies:

public MappingTests()
{
  _configuration = new MapperConfiguration(cfg => cfg.AddProfile<MappingProfile>());

  var services = new ServiceCollection()
      .AddAutoMapper(typeof(MappingProfile).Assembly)
      .RegisterDataTableUtilities()
      .BuildServiceProvider();

  _mapper = services.GetService<IMapper>();
}

Hopefully this will help someone who comes across a similar issue, or perhaps this might become a part of the template.