should_not

  receiver.should_not(matcher)
    => Passes unless matcher.matches?(receiver)

  receiver.should_not == expected
    => Passes unless (receiver == expected)

  receiver.should_not === expected
    => Passes unless (receiver === expected)

  receiver.should_not =~ regexp
    => Passes unless (receiver =~ regexp)

See Spec::Matchers for more information about matchers