caboose

UPDATE: Aslak noted that I'm not actually using mocks but stubs. The distinction appears to be in the use of expectations set on your mock object. Anyway, read more at [Martin Fowler's Bliki](http://www.martinfowler.com/articles/mocksArentStubs.html). So the classic rails example: you're writing a blog. Maybe you've decided you want to be able to add feeds of your buddies Slash and Dingo to your sidebar so that their latest content shows up there. You sit down to bang out code but because you're working to improve your code practices you decide to write tests first. How do you write tests against information that might change or you don't always have access to in development? Stubbing to the rescue. Stubs are a bit like fixtures outside of the database. We have some sort of information that our queries should return, so we stub those responses and are able to run our tests on our code without changing the application. In our case, we're using something like this in our blog model to fetch our RSS feed and parse it.

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def fetch uri = URI.parse(self.rss_url) http = Net::HTTP.new(uri.host,uri.port) if !uri.query.nil? rss = SimpleRSS.parse http.get(uri.path + '?' + uri.query, 'User-Agent' => 'glu.ttono.us/1.0').body else rss = SimpleRSS.parse http.get(uri.path, 'User-Agent' => 'glu.ttono.us/1.0').body end end

When we run tests the application shouldn't actually hit the website, so we'll stub out the methods that do that. In our case, Net::HTTP.get (Note: Net::HTTP.new doesn't actually make a connection). What we'd like is to be able to have the request actually return information in a file that we've defined, so the call to get should return the file and the call to body should give us the contents. Here's an easy way to implement that.

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require 'net/http' module Net class HTTP def get(path, *args) return File.open("#{RAILS_ROOT}/test/mocks/test/#{File.basename(path)}") end end end class File alias_method :body, :read end

Shove it in your test/mocks/test directory, and write your test cases. For example:

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require File.dirname(__FILE__) + '/../test_helper' require File.dirname(__FILE__) + '/../mocks/test/http' class BlogTest < Test::Unit::TestCase fixtures :blogs, :items def test_fetch num_items = Item.count b = blogs(:gluttonous_with_sample_feed) assert_equal 0, b.items.count b.fetch assert_equal num_items + 10, Item.count assert_equal 10, b.items.count end end

See Scott Baron's article [Mockery](http://scott.elitists.net/users/scott/posts/mockery) for information on Mocks (no, not stubs) in a more general Ruby sense.