# File activesupport/lib/active_support/testing/time_helpers.rb, line 234
def freeze_time(&block)
  travel_to Time.now, &block
end

Calls travel_to with Time.now.

Time.current # => Sun, 09 Jul 2017 15:34:49 EST -05:00
freeze_time
sleep(1)
Time.current # => Sun, 09 Jul 2017 15:34:49 EST -05:00

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 # => Sun, 09 Jul 2017 15:34:49 EST -05:00
freeze_time do
  sleep(1)
  User.create.created_at # => Sun, 09 Jul 2017 15:34:49 EST -05:00
end
Time.current # => Sun, 09 Jul 2017 15:34:50 EST -05:00

# File activesupport/lib/active_support/testing/time_helpers.rb, line 93
def travel(duration, &block)
  travel_to Time.now + duration, &block
end

Changes current time to the time in the future or in the past by a given time difference by stubbing Time.now, Date.today, and DateTime.now. The stubs are automatically removed at the end of the test.

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
DateTime.current # => Sun, 10 Nov 2013 15:34:49 -0500

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 208
def travel_back
  stubbed_time = Time.current if block_given? && simple_stubs.stubbed?

  simple_stubs.unstub_all!
  yield if block_given?
ensure
  travel_to stubbed_time if stubbed_time
end

Returns the current time back to its original state, by removing the stubs added by travel, travel_to, and freeze_time.

Time.current # => Sat, 09 Nov 2013 15:34:49 EST -05:00

travel_to Time.zone.local(2004, 11, 24, 1, 4, 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

This method also accepts a block, which brings the stubs back at the end of the block:

Time.current # => Sat, 09 Nov 2013 15:34:49 EST -05:00

travel_to Time.zone.local(2004, 11, 24, 1, 4, 44)
Time.current # => Wed, 24 Nov 2004 01:04:44 EST -05:00

travel_back do
  Time.current # => Sat, 09 Nov 2013 15:34:49 EST -05:00
end

Time.current # => Wed, 24 Nov 2004 01:04:44 EST -05:00

# File activesupport/lib/active_support/testing/time_helpers.rb, line 128
      def travel_to(date_or_time)
        if block_given? && in_block
          travel_to_nested_block_call = <<~MSG

      Calling `travel_to` with a block, when we have previously already made a call to `travel_to`, can lead to confusing time stubbing.

      Instead of:

         travel_to 2.days.from_now do
           # 2 days from today
           travel_to 3.days.from_now do
             # 5 days from today
           end
         end

      preferred way to achieve above is:

         travel 2.days do
           # 2 days from today
         end

         travel 5.days do
           # 5 days from today
         end

          MSG
          raise travel_to_nested_block_call
        end

        if date_or_time.is_a?(Date) && !date_or_time.is_a?(DateTime)
          now = date_or_time.midnight.to_time
        elsif date_or_time.is_a?(String)
          now = Time.zone.parse(date_or_time)
        else
          now = date_or_time.to_time.change(usec: 0)
        end

        stubbed_time = Time.now if simple_stubs.stubbing(Time, :now)
        simple_stubs.stub_object(Time, :now) { at(now.to_i) }
        simple_stubs.stub_object(Date, :today) { jd(now.to_date.jd) }
        simple_stubs.stub_object(DateTime, :now) { jd(now.to_date.jd, now.hour, now.min, now.sec, Rational(now.utc_offset, 86400)) }

        if block_given?
          begin
            self.in_block = true
            yield
          ensure
            if stubbed_time
              travel_to stubbed_time
            else
              travel_back
            end
            self.in_block = false
          end
        end
      end

Changes current time to the given time by stubbing Time.now, Date.today, and DateTime.now to return the time or date passed into this method. The stubs are automatically removed at the end of the test.

Time.current     # => Sat, 09 Nov 2013 15:34:49 EST -05:00
travel_to Time.zone.local(2004, 11, 24, 1, 4, 44)
Time.current     # => Wed, 24 Nov 2004 01:04:44 EST -05:00
Date.current     # => Wed, 24 Nov 2004
DateTime.current # => Wed, 24 Nov 2004 01:04:44 -0500

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.)

Note that the usec for the time passed will be set to 0 to prevent rounding errors with external services, like MySQL (which will round instead of floor, leading to off-by-one-second errors).

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.zone.local(2004, 11, 24, 1, 4, 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