public MusicController(
     IArtistService artistService,
     IAggregatorProcess aggregatorProcess,
     ICacheService cacheService)
 {
     _artistService     = artistService ?? throw new ArgumentNullException(nameof(artistService));
     _aggregatorProcess = aggregatorProcess ?? throw new ArgumentNullException(nameof(aggregatorProcess));
     _cacheService      = cacheService ?? throw new ArgumentNullException(nameof(cacheService));
 }
            public SutContext()
            {
                var works = new Dictionary <Guid, Dictionary <Guid, ArtistWork> >();

                CacheService.Setup(x => x.Works).Returns(works);
                Process = new AggregatorProcess(
                    LyricsService.Object,
                    ArtistService.Object,
                    WordCounterService.Object,
                    CacheService.Object
                    );
            }