> I've run into the same problem and I did exactly what you're suggesting.
> You don't want to slow down your tests by making external API calls and
> since I'm assuming that you already know the behavior of the YouTube
> API, it makes sense to mimic that behavior in a mock class. Also, you
> will get great coverage results by doing this :)

When mocking an API, I often write a test like this:

  def toast_youtuber
    yt = YouTuber.new
    puts yt.fetch('some_feed')
  end

It's a "toast" - a temporary test that will toast your test run if you 
accidentally integrate it. Switch it from "toast" to "test" in your editor, 
run it, and inspect the output.

Switch it back to "toast", and copy the output into a sample file. Stash 
that in your test/fixtures folder, and use it when you mock the wire 
connection.

  def test_youtuber_fetch
     yt = YouTuber.new
     yt.expects(:fetch).returns(File.read(RAILS_ROOT + 
'/test/fixtures/youtuber.xml'))
     yt.fetch('some_feed')
     assert{ yt.feed == 'some_data' }
  end

The .expects is a Mocha mock. Note we don't mock the whole object - just the 
low-level part that hits the wire. (Unit tests that hit any outgoing wires 
are not just slow, they are evil.)

Whenever you need to upgrade your mock data, just turn on the toast test 
again and pull another real feed.

-- 
  Phlip