Random ActionView::Template::Error raised by RSpec but not in-browser

I have a few RSpec examples that I wrote to test various aspects of the rendered HTML as generated by a controller. These include things like...

it "should be successful" do
  get :show, :section => @section.slug
  response.should be_success
end

it "should have the right title" do
  get :show, :section => @section.slug
  response.should have_selector("title", :content => @section.name)
end

it "should find the right section" do
  get :show, :section => @section.slug
  assigns(:section).should == @section
end

These are testing SectionsController#show. When I navigate to the page in my browser, it is rendered perfectly, with no exceptions raised. However, RSpec returns (for all three, mind you):

Failure/Error: get :show, :section => @section.slug
ActionView::Template::Error

This is obviously failing on the line get :show, :section => @section.slug for all of the tests.

I have narrowed down the issue to one partial. In the view file for this action, I included a partial with

<%= render 'popular' %>

...and when this line is removed, all the tests pass. The relevant content for this partial is:

<div class="most_popular group">
    <%= render post_excerpt(@popular.shift, :class => "one") %>
</div><!-- end most popular -->

That post_excerpt is a helper method I wrote to return some parameters as a hash to be passed to render.

def post_excerpt(post, options)
  { :partial => 'posts/post_excerpt', :object => post, :as => :post, :locals => { :klass => options[:class] } }
end
开发者_运维问答

The partial 'posts/post_excerpt':

<article class="<%= klass if klass %>">
    <h2><%= link_to post.name, section_post_path(post.section, post) %></h2>
    <footer>By <%= link_to post.author.name, post.author %></footer>
    <hr />
    <div class="content">
        <%= raw(post.excerpt) %>
    </div><!-- end content -->
</article>

I am running RSpec 2.4.0 and Rails 3.0.3. I can provide more details or code snippets if needed, but I think this is enough to go on.

If you have any idea what might be causing this strange issue, please post it! Thanks!