block_helper.rb

# So you might have something like this:

# <% @presenter.tweets.each do |tweet| %>
#   <div id="tweet_#{tweet.id}" class="<%= 'favorite' if current_user && tweet.is_a_favorite?(current_user) %>">
#     <%= tweet.status %> 
#   </div>
# <% end %>

# Kinda ugly... this is a simple example of where you might want a block helper so our view becomes:

# <% tweet_div(tweet) do %> 
#   <%= tweet.status %>
# <% end %>

# then we have a helper 

  def tweet_div(tweet, &block)
    klass = 'favorite' if current_user && tweet.is_a_favorite?(current_user) 
      
    div_for tweet, :class => klass do
      yield
    end
  end

# if we wanted to make it even more testable, we might do

  def tweet_div(tweet, &block)      
    div_for tweet, :class => tweet_class(tweet) do
      yield
    end
  end
  
  def tweet_class(tweet)
    'favorite' if current_user && tweet.is_a_favorite?(current_user) 
  end