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

# File activesupport/lib/active_support/testing/time_helpers.rb, line 60
def travel(duration, &block)
  travel_to Time.now + duration, &block
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

# File activesupport/lib/active_support/testing/time_helpers.rb, line 116
def travel_back
  simple_stubs.unstub_all!
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. Time.current returns said timestamp, and Time.now its equivalent in the system time zone. Similarly, Date.current returns a date equal to the argument, and Date.today the date according to Time.now, which may be different. (Note that you rarely want to deal with Time.now, or Date.today, in order to honor the application time zone please always use Time.current and Date.current.)

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

# File activesupport/lib/active_support/testing/time_helpers.rb, line 89
def travel_to(date_or_time, &block)
  if date_or_time.is_a?(Date) && !date_or_time.is_a?(DateTime)
    now = date_or_time.midnight.to_time
  else
    now = date_or_time.to_time
  end

  simple_stubs.stub_object(Time, :now, now)
  simple_stubs.stub_object(Date, :today, now.to_date)

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