require 'test/unit' class TestVariable < Test::Unit::TestCase class Gods @@rule = "Uranus" def ruler0 @@rule end def self.ruler1 # <= per method definition style @@rule end class << self # <= multiple method definition style def ruler2 @@rule end end end module Olympians @@rule ="Zeus" def ruler3 @@rule end end class Titans < Gods @@rule = "Cronus" # modifies @@rule in Gods include Olympians def ruler4 @@rule end end def test_variable assert_instance_of(Fixnum, $$) # read-only variable assert_raises(NameError) do $$ = 5 end foobar = "foobar" $_ = foobar assert_equal(foobar, $_) assert_equal("Cronus", Gods.new.ruler0) assert_equal("Cronus", Gods.ruler1) assert_equal("Cronus", Gods.ruler2) assert_equal("Cronus", Titans.ruler1) assert_equal("Cronus", Titans.ruler2) atlas = Titans.new assert_equal("Cronus", atlas.ruler0) assert_equal("Zeus", atlas.ruler3) assert_equal("Cronus", atlas.ruler4) end end