Unit testing with and without requiring ActiveSupport - ruby

Question

I've extracted a single class from a Rails app into a gem. It's very, very simple, but of course I'd like to fully test it (I'm using rspec).
The class does some simple date-calculation. It's not dependent on Rails, but since it started out in a Rails app, and is still used there, it uses ActiveSupport's time zone-aware methods when it can. But, if ActiveSupport isn't available, it should use the std-lib Date methods.
Specifically, it only does this in one single place: Defaulting an optional argument to "today's date":
arg ||= if Date.respond_to?(:current)
Date.current # use ActiveSupport's time zone-aware mixin if possible
else
Date.today # stdlib fallback
end
Question is: How do I properly test this? If I require ActiveSupport in my spec_helper.rb, it'll obviously always use that. If I don't require it anywhere, it'll never use it. And if I require it for a single example group, rspec's random execution order makes the testing unpredictable, as I don't know when AS will be required.
I can require maybe it in a before(:all) in a nested group, as nested groups are (I believe) processed highest to deepest. But that seems terribly inelegant.
I could also split the specs into two files, and run them separately, but again, that seems unnecessary.
I could also disable rspec's random ordering, but that's sort of going against the grain. I'd rather have it as randomized as possible.
Any ideas?

Answer 1

Another solution is to mock the current and today methods, and use those for testing. Eg:
# you won't need these two lines, just there to make script work standalone
require 'rspec'
require 'rspec/mocks/standalone'
def test_method(arg = nil)
arg ||= if Date.respond_to?(:current)
Date.current # use ActiveSupport's time zone-aware mixin if possible
else
Date.today # stdlib fallback
end
arg
end
describe "test_method" do
let(:test_date) { Date.new(2001, 2, 3) }
it "returns arg unchanged if not nil" do
test_method(34).should == 34
end
context "without Date.current available" do
before(:all) do
Date.stub(:today) { test_date }
end
it "returns Date.today when arg isn't present" do
test_method.should == test_date
end
end
context "with Date.current available" do
before(:all) do
Date.stub(:current) { test_date }
end
it "returns Date.current when arg isn't present" do
test_method.should == test_date
end
end
end
Running with rspec test.rb results in the tests passing.
Also, the stubs are present only in each context, so it doesn't matter what order the specs are run in.

Answer 2

This is more than a little perverse, but it should work. Include ActiveSupport, and then:
context "without ActiveSupport's Date.current" do
before(:each) do
class Date
class << self
alias_method :current_backup, :current
undef_method :current
end
end
end
# your test
after(:each) do
class Date
class << self
alias_method :current, :current_backup
end
end
end
end
I can't really recommend this; I would prefer to split out this one spec and run it separately as you suggested.