Rails Time Travel Revisited: Manipulating Time.now for Specs

A few month ago I wrote about how to manipulate Time.now for your Rails Test::Unit tests. I've switched to using RSpec since then and had the same problem again: I have code that uses Time.now and I want to test it. It was fairly easy to move the code from Test::Unit to RSpec:

1. Copy the following code into spec/time_spec_helper.rb

   unless Time.respond_to? :real_now   # prevent the error: stack level too deep (SystemStackError)
   # <b>Test Helper: used only in testing!</b>
   #
   # Extend the  Time  class so that we can offset the time that  now
   # returns. This should allow us to effectively time warp for functional
   # tests that require limits per hour, what not.
   #
   # Example usage:
   #   require File.expand_path(File.dirname(__FILE__)   '/../spec_helper')
   #   require File.expand_path(File.dirname(__FILE__)   '/../time_spec_helper')
   #
   #   describe YourModel do
   # 
   #     before(:each) do
   #       pretend_now_is(Time.local(1999, 8, 1))  # position *all* tests back in time!
   #     end
   # 
   #     after(:each) do
   #       Time.reset    # jump back to the present
   #     end
   #
   #     it "should be 1999" do
   #       Time.now.year.should == 1999
   #     end
   #
   #     # If one particular spec needs some time jumping of its own...
   #     it "should jump to decades" do
   #       pretend_now_is(Time.local(1960)) do
   #         Time.now.year.should == 1960
   #       end
   #
   #       pretend_now_is(Time.local(1970)) do
   #         Time.now.year.should == 1970
   #       end
   #     end
   #     # ...
   #   end
   #
   #
   # <em><tt>(see reference http://snippets.dzone.com/posts/show/1738)</tt></em>
   class Time
     class <<self
       attr_reader :offset
       alias_method :real_now, :now
       def now
         @offset = 0 if @offset.nil?
         real_now - @offset
       end
       alias_method :new, :now
   
       # Warp to an absolute  time  in the past or future, making sure it takes
       # the present as the reference starting point when making the jump.
       def set(time)
         reset
         @offset = now - time
       end
   
       # Jump back to present.
       def reset
         @offset = 0
       end
     end
   end
   end
     
   # Time warp to the specified  time . If given a block, it applies only for the
   # duration of the passed block.
   def pretend_now_is(time)
   Time.set(time)
   if block_given?
     begin
       yield
     ensure
       Time.reset
     end
   end
   end

2. Require it in your spec:

   require File.expand_path(File.dirname(__FILE__) + '/../time_spec_helper')

3. Travel through time in your specs:

   before(:each) do
     pretend_now_is(Time.local(1999, 8, 1))  # position *all* tests back in time!
   end
   
   after(:each) do
     Time.reset    # jump back to the present
   end
   
   it "should be 1999" do
     Time.now.year.should == 1999
   end
   
   # If one particular spec needs some time jumping of its own...
   it "should jump to decades" do
     pretend_now_is(Time.local(1960)) do
       Time.now.year.should == 1960
     end
   
     pretend_now_is(Time.local(1970)) do
       Time.now.year.should == 1970
     end
   end

4. Enjoy.

Please note that this code is based on this highly useful piece of code.

If this was useful for you, please take a minute and recommend me: Thank you!

---

Comments