Rails Time inconsistencies with rspec

Question

I'm working with Time in Rails and using the following code to set up the start date and end date of a project:

start_date ||= Time.now
end_date = start_date + goal_months.months

I then clone the object and I'm writing rspec tests to confirm that the attributes match in the copy. The end dates match:

original[end_date]:  2011-08-24 18:24:53 UTC
clone[end_date]:     2011-08-24 18:24:53 UTC

but the spec gives me an error on the start dates:

expected: Wed Aug 24 18:24:53 UTC 2011,
     got: Wed, 24 Aug 2011 18:24:53 UTC +00:00 (using ==)

It's clear the dates are the same, just formatted differently. How is it that they end up getting stored differently in the database, and how do I get them to match? I've tried it with DateTime as well with the same results.

Correction: The end dates don't match either. They print out the same, but rspec errors out on them as well. When I print out the start date and end date, the values come out in different formats:

start date: 2010-08-24T19:00:24+00:00
end date: 2011-08-24 19:00:24 UTC

Answer 1

This usually happens because rspec tries to match different objects: Time and DateTime, for instance. Also, comparable times can differ a bit, for a few milliseconds.

In the second case, the correct way is to use stubbing and mock. Also see TimeCop gem

In the first case, possible solution can be to compare timestamps:

actual_time.to_i.should == expected_time.to_i

I use simple matcher for such cases:

# ./spec/spec_helper.rb
#
# Dir[File.dirname(__FILE__) + "/support/**/*.rb"].each {|f| require f}
#
#
# Usage:
#
# its(:updated_at) { should be_the_same_time_as updated_at }
#
#
# Will pass or fail with message like:
#
# Failure/Error: its(:updated_at) { should be_the_same_time_as 2.days.ago }
# expected Tue, 07 Jun 2011 16:14:09 +0300 to be the same time as Mon, 06 Jun 2011 13:14:09 UTC +00:00


RSpec::Matchers.define :be_the_same_time_as do |expected|
  match do |actual|
    expected.to_i == actual.to_i
  end
end

Answer 2

You should mock the now method of Time to make sure it always match the date in the spec. You never know when a delay will make the spec fail because of some milliseconds. This approach will also make sure that the time on the real code and on the spec are the same.

If you're using the default rspec mock lib, try to do something like:

t = Time.parse("01/01/2010 10:00")
Time.should_receive(:now).and_return(t)

Answer 3

I totally agree with the previous answers about stubbing Time.now. That said there is one other thing going on here. When you compare datetimes from a database you lose some of the factional time that can be in a ruby DateTime obj. The best way to compare date in that way in Rspec is:

database_start_date.should be_within(1).of(start_date)

Answer 4

One gotcha is that Ruby Time objects have nanosecond precision, but most databases have at most microsecond precision. The best way to get around this is to stub Time.now (or use timecop) with a round number. Read the post I wrote about this: http://blog.solanolabs.com/rails-time-comparisons-devil-details-etc/