message: add test about artist
diff: @@ -2,6 +2,8 @@ extern crate rspotify;
  use rspotify::spotify::client::Spotify;
  use rspotify::spotify::oauth2::SpotifyClientCredentials;
  +use rspotify::spotify::senum::{AlbumType, Country};
  +
  #[test]
  fn test_album() {
  // Set client_id and client_secret in .env file or
  @@ -21,3 +23,63 @@ fn test_album() {
  let albums = spotify.album(birdy_uri);
  assert!(albums.is_ok());
  }
  +#[test]
  +fn test_albums() {
  + let client_credential = SpotifyClientCredentials::default().build();
  + let spotify = Spotify::default()
  + .client_credentials_manager(client_credential)
  + .build();
  + let birdy_uri1 = String::from("spotify:album:41MnTivkwTO3UUJ8DrqEJJ");
  + let birdy_uri2 = String::from("spotify:album:6JWc4iAiJ9FjyK0B59ABb4");
  + let birdy_uri3 = String::from("spotify:album:6UXCm6bOO4gFlDQZV5yL37");
  + let track_uris = vec![birdy_uri1, birdy_uri2, birdy_uri3];
  + let albums = spotify.albums(track_uris);
  + assert!(albums.is_ok())
  +}
  +#[test]
  +fn test_album_tracks() {
  + let client_credential = SpotifyClientCredentials::default().build();
  + let spotify = Spotify::default()
  + .client_credentials_manager(client_credential)
  + .build();
  + let birdy_uri = "spotify:album:6akEvsycLGftJxYudPjmqK";
  + let tracks = spotify.album_track(birdy_uri, Some(2), None);
  + assert!(tracks.is_ok());
  +}
  +
  +#[test]
  +fn test_artist_related_artists() {
  + let client_credential = SpotifyClientCredentials::default().build();
  + let spotify = Spotify::default()
  + .client_credentials_manager(client_credential)
  + .build();
  + let birdy_uri = "spotify:artist:43ZHCT0cAZBISjO8DG9PnE";
  + let artist = spotify.artist_related_artists(birdy_uri);
  + assert!(artist.is_ok())
  +}
  +
  +#[test]
  +fn test_artist() {
  + let client_credential = SpotifyClientCredentials::default().build();
  + let spotify = Spotify::default()
  + .client_credentials_manager(client_credential)
  + .build();
  + let birdy_uri = "spotify:artist:2WX2uTcsvV5OnS0inACecP";
  + let artist = spotify.artist(birdy_uri);
  + assert!(artist.is_ok());
  +}
  +
  +#[test]
  +fn test_artists_albums() {
  + let client_credential = SpotifyClientCredentials::default().build();
  + let spotify = Spotify::default()
  + .client_credentials_manager(client_credential)
  + .build();
  + let birdy_uri = "spotify:artist:2WX2uTcsvV5OnS0inACecP";
  + let albums = spotify.artist_albums(birdy_uri,
  + Some(AlbumType::Album),
  + Some(Country::UnitedStates),
  + Some(10),
  + None);
  + assert!(albums.is_ok());
  +}
  