Specs for Time#gmtime/Time#utc are insufficient

[herwinw]

These use a shared spec (time_gmtime) with tests like this:

it "converts self to UTC, modifying the receiver" do
  # Testing with America/Regina here because it doesn't have DST
  with_timezone("CST", -6) do
    t = Time.local(2007, 1, 9, 6, 0, 0)
    t.send(@method)
    t.should == Time.gm(2007, 1, 9, 12, 0, 0)
  end
end

It looks like the == (or <=>) method normalizes the time zones for comparison, although I could not find any reference to this in the specs or the documentation of the Time class.

If we alter the file gmtime_spec.rb to this:

describe "Time#gmtime" do
  it_behaves_like :time_gmtime, :itself
end

If we call it like this, we don't modify anything in the time object and this still passes most of these specs (the only failure is a spec for frozen input).

I guess we need to change two things:

• Add extra validations in shared/gmtime.rb to check the time zone of the object (this could be done with Time#utc?, but there might be a way without introducing an additional dependency)
• Validate the behaviour for Time comparison with time zones. Add this behaviour to the specs (and possible get it in the docs of Ruby)

I'm planning to take a look into this later this week, but if anybody feels inspired and want to tackle this: be my guest.