public async Task TestCreatePlaylist()
        {
            MusicLibraryService service = new MusicLibraryService();
            await Task.Delay(1000);

            service.CreatePlaylist("a");
            service.CreatePlaylist("a");
            Assert.IsTrue(service.Library.Playlists.Count(p => p.Name == "a") == 1);
            service.Clean();
        }
        public async Task TestSameSongOnMuliplePlaylist()
        {
            MusicLibraryService service = new MusicLibraryService();
            await Task.Delay(1000);

            service.CreatePlaylist("a");
            service.CreatePlaylist("b");
            Assert.IsTrue(service.Library.Playlists.Count == 2);
            var songs = service.Library.Musics;

            service.AddSongsToPlaylist("a", songs.ToList());
            service.AddSongsToPlaylist("b", songs.ToList());

            Assert.IsTrue(service.Library.MInP.Count == songs.Count * 2);

            service.Clean();
        }
        public async Task TestAddSongsIntoPlaylist()
        {
            MusicLibraryService service = new MusicLibraryService();
            await Task.Delay(1000);

            service.CreatePlaylist("a");
            Assert.IsTrue(service.Library.Playlists.Count(p => p.Name == "a") == 1);
            var songs = service.Library.Musics;

            service.AddSongsToPlaylist("a", songs.ToList());
            Assert.IsTrue(service.Library.MInP.Count == songs.Count);
            service.Clean();
        }