public IEnumerable <AssetFile> ResolveAssetFiles(IFileSystem fileSystem)
        {
            fileSystem.ThrowIfNull("fileSystem");

            string directory = fileSystem.AbsolutePath(_relativeDirectory);

            string[] paths = fileSystem.GetDirectoryFiles(directory, _searchPattern, _searchOption);

            return(paths
                   .Where(arg => _filter == null || _filter.Filter(arg) == FilterResult.Include)
                   .Select(arg => new AssetFile(arg, _encoding)));
        }