# this would be in a helper somewhere
def stub_find(entity)
  result = mock_model(entity)
  entity.stub(:find).with(result.id).and_return(result)
  result
end

let(:params) do
  {:these => 'params'}
end

it "updates the requested book" do
  mock_book = stub_find(Book)
  mock_book.should_receive(:update_attributes).with(params)
  put :update, :id => book.id, :book => params
end