Add `#travel` and `#travel_to` to AS::TestCase

Add `ActiveSupport::Testing::TimeHelpers#travel` and `#travel_to`. These
methods change current time to the given time or time difference by
stubbing `Time.now` and `Date.today` to return the time or date after
the difference calculation, or the time or date that got passed into the
method respectively. These methods also accept a block, which will
return current time back to its original state at the end of the block.

Example for `#travel`:

    Time.now # => 2013-11-09 15:34:49 -05:00
    travel 1.day
    Time.now # => 2013-11-10 15:34:49 -05:00
    Date.today # => Sun, 10 Nov 2013

Example for `#travel_to`:

    Time.now # => 2013-11-09 15:34:49 -05:00
    travel_to Time.new(2004, 11, 24, 01, 04, 44)
    Time.now # => 2004-11-24 01:04:44 -05:00
    Date.today # => Wed, 24 Nov 2004

Both of these methods also accept a block, which will return the current
time back to its original state at the end of the block:

    Time.now # => 2013-11-09 15:34:49 -05:00

    travel 1.day do
      User.create.created_at # => Sun, 10 Nov 2013 15:34:49 EST -05:00
    end

    travel_to Time.new(2004, 11, 24, 01, 04, 44) do
      User.create.created_at # => Wed, 24 Nov 2004 01:04:44 EST -05:00
    end

    Time.now # => 2013-11-09 15:34:49 -05:00

This module is included in `ActiveSupport::TestCase` automatically.

2 files changed, 57 insertions, 0 deletions

diff --git a/activesupport/lib/active_support/test_case.rb b/activesupport/lib/active_support/test_case.rb
index e193163d17..2fb5c04316 100644
--- a/activesupport/lib/active_support/test_case.rb
+++ b/activesupport/lib/active_support/test_case.rb
@@ -7,6 +7,7 @@ require 'active_support/testing/deprecation'
 require 'active_support/testing/declarative'
 require 'active_support/testing/isolation'
 require 'active_support/testing/constant_lookup'
+require 'active_support/testing/time_helpers'
 require 'active_support/core_ext/kernel/reporting'
 require 'active_support/deprecation'
 
@@ -34,6 +35,7 @@ module ActiveSupport
     include ActiveSupport::Testing::SetupAndTeardown
     include ActiveSupport::Testing::Assertions
     include ActiveSupport::Testing::Deprecation
+    include ActiveSupport::Testing::TimeHelpers
     extend ActiveSupport::Testing::Declarative
 
     # test/unit backwards compatibility methods
diff --git a/activesupport/lib/active_support/testing/time_helpers.rb b/activesupport/lib/active_support/testing/time_helpers.rb
new file mode 100644
index 0000000000..a95ba21ba4
--- /dev/null
+++ b/activesupport/lib/active_support/testing/time_helpers.rb
@@ -0,0 +1,55 @@
+module ActiveSupport
+  module Testing
+    # Containing helpers that helps you test passage of time.
+    module TimeHelpers
+      # Change current time to the time in the future or in the past by a given time difference by
+      # stubbing +Time.now+ and +Date.today+. This method also accepts a block, which will return
+      # 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
+      #   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
+
+      # Change current time to the given time by stubbing +Time.now+ and +Date.today+ to return the
+      # time or date passed into this method. This method also accepts a block, which will return
+      # 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)
+      #   Time.current # => Wed, 24 Nov 2004 01:04:44 EST -05:00
+      #   Date.current # => Wed, 24 Nov 2004
+      #
+      # 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
+      #     User.create.created_at # => 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)
+        Time.stubs now: date_or_time.to_time
+        Date.stubs today: date_or_time.to_date
+
+        if block_given?
+          block.call
+          Time.unstub :now
+          Date.unstub :today
+        end
+      end
+    end
+  end
+end