Add spec for not overwriting the image_url on profile update
user
```ruby
#   Copyright (c) 2010, Diaspora Inc.  This file is
#   licensed under the Affero General Public License version 3.  See
#   the COPYRIGHT file.

require 'spec_helper'

describe UsersController do
  before do
    @user = Factory.create(:user)
    sign_in :user, @user
    @user.aspect(:name => "lame-os")
  end

  describe '#update' do
    context 'with a profile photo set' do
      before do
        @user.person.profile.image_url = "http://tom.joindiaspora.com/images/user/tom.jpg"
        @user.person.profile.save
      end

      it "doesn't overwrite the profile photo when an empty string is passed in" do
        image_url = @user.person.profile.image_url
        put("update", :id => @user.id, "user"=> {"profile"=> 
          {"image_url"   => "",
            "last_name"  => @user.person.profile.last_name,
            "first_name" => @user.person.profile.first_name}})
        
        @user.person.profile.image_url.should == image_url
      end

    end
  end
end
```
assistant