instantiation and collections - ruby - ruby

Question

I am a newb and struggling with making a test pass. I have 3 classes, artists, songs, and genres. The test I am trying to make pass is below:
test 'A genre has many artists' do
genre = Genre.new.tap{|g| g.name = 'rap'}
[1,2].each do
artist = Artist.new
song = Song.new
song.genre = genre
artist.add_song(song)
end
assert_equal genre.artists.count, 2
end
This is my artist class, the add_song method is the one I need to tweak. When a song is added to an artist I am trying to instantiate a new Genre object and add the artist to that genre as well. Currently not working though, when I call genre.artists it returns an empty array.
class Artist
attr_accessor :name, :songs, :genres, :genre, :artists
##artists = []
def initialize(name = name, genre = genre)
#artists = []
#songs = []
#genre = genre
#genres = []
#name = name
##artists << self
end
def self.all
##artists
end
def self.reset_artists
##artists = []
end
def self.count
self.all.size
end
def songs_count
self.songs.size
end
def count
self.size
end
def add_song(song)
#songs << song
#genres << song.genre
Genre.new(self)
end
end
class Genre
attr_accessor :name, :songs, :artists
##genres = []
def initialize(artists = artists)
#songs = []
#artists = artists
#name = name
##genres << self
end
def count
self.artists.count
end
def self.all
##genres
end
def self.reset_genres
##genre = []
end
end
class Song
attr_accessor :name, :genre, :artist
def initialize(name = name, artist = artist, genre = genre)
#name = name
#artist = artist
#genre = genre
end
end

Answer 1

When you create a new artist, you add it to Artist::artists - a class variable of Artist. The array you test is genre.artists - an object variable of Genre. That's a different variable from Artist::artists, and I don't see you updating genre.artists anywhere in your code - I'm surprised it's even an array, seeing that you don't initialize it to an array...

Answer 2

You are returning a creating a new instance of Genre with the current artist in the add_song method. You could get your test to pass in a couple of ways.
This will add an artist to the genre referenced in the song instance.
def add_song(song)
#songs << song
#genres << song.genre
song.genre.artists << self
end
The second option would be fix your test if you want to return a new Genre instance from your add_song method. This is most likely not what you want, however this would set artist the reference in Genre.
test 'A genre has many artists' do
genre = Genre.new.tap{|g| g.name = 'rap'}
[1,2].each do
art ist = Artist.new
song = Song.new
song.genre = genre
genre = artist.add_song(song)
end
assert_equal genre.artists.count, 2
end