time_greeter.rb

class TimeGreeter
  def initialize(time = Time.now)
    @time = time.hour
  end

  def greet
    puts "At the tone, the time of day is #{hour_word}"
  end

  private

    def hour_word
      return "morning" if @time < 12
      return "night" if @time > 18
      "afternoon"
    end
end

 TimeGreeter.new.greet # => Will change over time, may require a gem like TimeCop


 # See here I can "inject" a time.  I can "stub" in a value (some arbitrary
 # test data) and make sure that the algorithm in TimeGreeter works.
 TimeGreeter.new(Time.new(2002, 10, 31, 2, 2, 2, "+02:00")).greet
 TimeGreeter.new(Time.new(2002, 10, 31, 22, 22, 22, "+02:00")).greet

 # Thus you can imagine in an RSpec test that....
 #
 # do "test where i don't need timecop" do
 #   it "does the right thing" do
 #     expect(TimeGreeter.new(Time.new(2002, 10, 31, 22, 22, 22,
 #     "+02:00")).greet).to eq "At the tone, the time of day is night"
 #   end
 # end