Functional Test has error when testing controller updates_attribute of its parrent.

I am working in Rails 2.0 and I have the following functional test.

class VotesControllerTest < ActionController::TestCase
  def test_should_create_vote
    assert_difference('Vote.count') do
      post :create, {:vote => {:vote_value => 5,
                              :user_id => users(:nick).id,
                              :entry_id => entries(:BmxEntry).id}},
                    :user_id => users(:nick).id
    end
    assert_redirected_to vote_path(assigns(:vote))
  end
end

This tests the :create action of the vote controller which looks like
this.
  def create
    @vote = Vote.new(params[:vote])

    respond_to do |format|
      if @vote.save

        # Update the entry vote count and vote total columns
        @vote.entry.vote_count ||= 0
        @vote.entry.vote_total ||= 0
        @vote.entry.vote_count += 1
        @vote.entry.vote_total += @vote.vote_value
        @vote.entry.update_attribute(:vote_count,
@vote.entry.vote_count)
        @vote.entry.update_attribute(:vote_total,
@vote.entry.vote_total)

        flash[:notice] = 'Vote was successfully created.'
        format.html { redirect_to(@vote)}
        format.xml { render :xml => @vote, :status
=> :created, :location => @vote }
      else
        format.html { render :action => "new", :layout => false }
        format.xml { render :xml => @vote.errors, :status
=> :unprocessable_entity }
      end
    end
  end

As you can see, after the vote is created the vote's parent, entry, is
updated to reflect the new vote. All the associations are set up where
entry has_many :votes and vote belongs_to :entry. This code works just
fine when working in development, but the test fails giving this
error:

NoMethodError: You have a nil object when you didn't expect it!
The error occurred while evaluating nil.value

If I comment out the two following lines that update_attribute then
the test succeeds.

    # @vote.entry.update_attribute(:vote_count,
@vote.entry.vote_count)
    # @vote.entry.update_attribute(:vote_total,
@vote.entry.vote_total)

I am not sure what is causing this error, I checked and @vote.entry is
set and entry attributes are available. Any ideas on what may be
causing this.

A little extra information,

Here is the end of the error message showing where I stopped:

c:/ruby/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/
test_process.rb:15:in `process'
c:/ruby/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/
test_process.rb:393:in `process'
c:/ruby/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/
test_process.rb:364:in `post'
test/functional/votes_controller_test.rb:11:in
`test_should_create_vote'
c:/ruby/lib/ruby/gems/1.8/gems/mocha-0.5.6/lib/mocha/
test_case_adapter.rb:19:in `__send__'
c:/ruby/lib/ruby/gems/1.8/gems/mocha-0.5.6/lib/mocha/
test_case_adapter.rb:19:in `run'
c:/ruby/lib/ruby/gems/1.8/gems/activesupport-2.0.2/lib/active_support/
testing/default.rb:7:in `run'

And if I look at my test database after the test I see that a vote was
created, and the entry was updated, just as I would like it too. So
those calls are working but something about the @vote.entry.update
causes the test to error.