anchor.diff:  verse_test() ->
     compare_nested_lists(beer_song:verse(8),
                          "8 bottles of beer on the wall, 8 bottles of beer.\n"
  -                       "Take it down and pass it around, 7 bottles of beer on the wall.\n").
  +                       "Take one down and pass it around, 7 bottles of beer on the wall.\n").
   
   verse_0_test() ->
     compare_nested_lists(beer_song:verse(0),
  
positive.code: 
  compare_nested_lists(Response, Expected) ->
    ?assertEqual(lists:flatten(Expected), lists:flatten(Response)).
  
  
negative.code: verse_2_test() ->
    compare_nested_lists(beer_song:verse(2),
                         "2 bottles of beer on the wall, 2 bottles of beer.\n"
                         "Take one down and pass it around, 1 bottle of beer on the wall.\n").
  
  singing_several_verses_test() ->
    compare_nested_lists(beer_song:sing(8, 6),
                         "8 bottles of beer on the wall, 8 bottles of beer.\n"
                         "Take one down and pass it around, 7 bottles of beer on the wall.\n\n"
  
                         "7 bottles of beer on the wall, 7 bottles of beer.\n"
                         "Take one down and pass it around, 6 bottles of beer on the wall.\n\n"
  
                         "6 bottles of beer on the wall, 6 bottles of beer.\n"
                         "Take one down and pass it around, 5 bottles of beer on the wall.\n\n").
  
  sing_all_the_rest_of_the_verses_test() ->
    compare_nested_lists(beer_song:sing(3),
                         "3 bottles of beer on the wall, 3 bottles of beer.\n"
                         "Take one down and pass it around, 2 bottles of beer on the wall.\n\n"
  
                         "2 bottles of beer on the wall, 2 bottles of beer.\n"
                         "Take one down and pass it around, 1 bottle of beer on the wall.\n\n"
  
                         "1 bottle of beer on the wall, 1 bottle of beer.\n"
                         "Take it down and pass it around, no more bottles of beer on the wall.\n\n"
  