Rails testing: session mechanism creates new cart instead of using fixture

I am new to Rails and am following the 'Agile Web Devel开发者_开发技巧opment with Rails' book. Currently I am testing my cart and line items.

In my fixtures I have 2 line items. I delete one in the test, so one more remains in the cart. However I think due to my session mechanism the controller now uses a new empty cart instead of the fixture cart. This caused my test to fail.

In my *application_controller.rb*

  def current_cart
    Cart.find(session[:cart_id])
  rescue ActiveRecord::RecordNotFound
    cart = Cart.create
    session[:cart_id] = cart.id
    cart
  en

In my *line_items_controller.rb* I have:

def destroy @line_item = LineItem.find(params[:id]) @line_item.destroy

respond_to do |format|
  if current_cart.line_items.empty?
    format.html { redirect_to(store_url, :notice => 'Your cart is empty') }
  else
    format.html { redirect_to(current_cart, :notice => 'Item removed' )}
  end
  format.xml  { head :ok }
end

end

And in my *functional\line_items_controller_test.rb* I have:

  test "should destroy line_item" do
    assert_difference('LineItem.count', -1) do
      delete :destroy, :id => @line_item.to_param
    end
    assert(!@cart.line_items.empty?,'Cart should not be empty')
    if @cart.line_items.empty?
      assert_redirected_to store_url              #this was the redirection result
    else
      assert_redirected_to cart_path(@cart.id)    #but should be this redirection
    end
  end

The code works in real environment, just that the test fails.

How can I modify my test & code, so fixture-cart and my session mechanism can work together and pass the test?

The controller action takes a second hash of session variables to use for the request.

delete :destroy, { :id => @line_item.to_param }, { :cart_id => @cart.id }