time_helpers.rb

class Time
  class << self
    def now_with_travel
      Thread.current[:travelled_to] || now_without_travel
    end

    alias_method_chain :now, :travel
  end
end

class Date
  class << self
    def today_with_travel
      Thread.current[:travelled_to].try(:to_date) || today_without_travel
    end

    alias_method_chain :today, :travel
  end
end

module ActiveSupport
  module Testing
    # Containing helpers that helps you test passage of time.
    module TimeHelpers
      # Changes current time to the time in the future or in the past by a given time difference by
      # stubbing +Time.now+ and +Date.today+.
      #
      #   Time.current # => Sat, 09 Nov 2013 15:34:49 EST -05:00
      #   travel 1.day
      #   Time.current # => Sun, 10 Nov 2013 15:34:49 EST -05:00
      #   Date.current # => Sun, 10 Nov 2013
      #
      # This method also accepts a block, which will return the current time back to its original
      # state at the end of the block:
      #
      #   Time.current # => Sat, 09 Nov 2013 15:34:49 EST -05:00
      #   travel 1.day do
      #     User.create.created_at # => Sun, 10 Nov 2013 15:34:49 EST -05:00
      #   end
      #   Time.current # => Sat, 09 Nov 2013 15:34:49 EST -05:00
      def travel(duration, &block)
        travel_to Time.now + duration, &block
      end

      # Changes current time to the given time by stubbing +Time.now+ and
      # +Date.today+ to return the time or date passed into this method.
      #
      #   Time.current # => Sat, 09 Nov 2013 15:34:49 EST -05:00
      #   travel_to Time.new(2004, 11, 24, 01, 04, 44)
      #   Time.current # => Wed, 24 Nov 2004 01:04:44 EST -05:00
      #   Date.current # => Wed, 24 Nov 2004
      #
      # Dates are taken as their timestamp at the beginning of the day in the
      # application time zone. <tt>Time.current</tt> returns said timestamp,
      # and <tt>Time.now</tt> its equivalent in the system time zone. Similarly,
      # <tt>Date.current</tt> returns a date equal to the argument, and
      # <tt>Date.today</tt> the date according to <tt>Time.now</tt>, which may
      # be different. (Note that you rarely want to deal with <tt>Time.now</tt>,
      # or <tt>Date.today</tt>, in order to honor the application time zone
      # please always use <tt>Time.current</tt> and <tt>Date.current</tt>.)
      #
      # This method also accepts a block, which will return the current time back to its original
      # state at the end of the block:
      #
      #   Time.current # => Sat, 09 Nov 2013 15:34:49 EST -05:00
      #   travel_to Time.new(2004, 11, 24, 01, 04, 44) do
      #     Time.current # => Wed, 24 Nov 2004 01:04:44 EST -05:00
      #   end
      #   Time.current # => Sat, 09 Nov 2013 15:34:49 EST -05:00
      def travel_to(date_or_time, &block)
        if date_or_time.is_a?(Date) && !date_or_time.is_a?(DateTime)
          Thread.current[:travelled_to] = date_or_time.midnight.to_time
        else
          Thread.current[:travelled_to] = date_or_time.to_time
        end

        if block_given?
          begin
            block.call
          ensure
            travel_back
          end
        end
      end

      # Returns the current time back to its original state, by removing the stubs added by
      # `travel` and `travel_to`.
      #
      #   Time.current # => Sat, 09 Nov 2013 15:34:49 EST -05:00
      #   travel_to Time.new(2004, 11, 24, 01, 04, 44)
      #   Time.current # => Wed, 24 Nov 2004 01:04:44 EST -05:00
      #   travel_back
      #   Time.current # => Sat, 09 Nov 2013 15:34:49 EST -05:00
      def travel_back
        Thread.current[:travelled_to] = nil
      end
    end
  end
end