SpecTunes

Using pair test-driven development with RSpec, create the following classes:

Track

• Has a title, list of artists (order doesn't matter), duration, and price
• Has a "set discount" method that reduces the price by a given percentage
• Has a "reset discount" method that restores the price to its original value

Note: The "set discount" method should not return a discounted price – it should actually change the price of the track. If I create a track with price 1.0 and I call track.set_discount(0.2), subsequent calls to track.price should now return 0.8. If I apply another discount, it should replace the previous discount rather than stacking onto it.

Album

• Has a title and a list of Track objects (order matters)
• Has a duration (combined duration of all tracks)
• Has a price (combined price of all tracks)
• Has a list of artists (combined artists of all tracks in alphabetical order – no duplicates)
• Can determine whether the album is a single (has exactly one track)

Next Steps

Still using test-driven development, add some data validation to these classes. For instance, I probably shouldn't be able to create an album with no tracks, or set a track's discount greater than 100%. Think of ways someone could abuse your code – what happens if I try to create a track with the "list of artists" set to 42? Generally it's appropriate to raise ArgumentError when your methods receive invalid data as an argument.