gistfile1.rb

# code
class ExternalDataApi
  def initialize(setup)
    # do stuff to setup
  end

  def list_of_things
    # grabs stuff from the api and returns an array of OStructs
  end
end


class Thing << ActiveRecord::Base

  def self.load_stuff_from_api
    api = ExternalDataApi.new(setup)
    api.list_of_things.each do |thing|
      Stuff.create(
        :name => thing.name,
        :etc  => thing.etc
      )
    end
  end

end


# spec
describe Thing, ".load_stuff_from_api" do
  before(:each) do
    @mock_api = mock('ExternalDataApi', :list_of_things => [])
    ExternalDataApi.stub!(:new).and_return @mock_api
  end

  it "initializes an ExternalDataApi with blah blah" do
    # expect
    ExternalDataApi.should_receive(:new).with('expected setup') # the stub from above will return @mock_api
    # when
    Thing.load_stuff_from_api
  end

  it "populates things from the api" do
    fake_list = [OpenStruct.new(:name => "name", :etc => "etc")]

    @mock_api.stub!(:list_of_things).and_return(fake_list)

    Thing.count.should == 0 # this is really a sanity check and is optional since you should have a clean state at this point
    Thing.load_stuff_from_api
    Thing.all.map { |things| things.attributes.slice(:name, :etc) }.should == fake_list.map { |s| { :name => s.name, :etc => s.etc } }
  end
end