Index: app/controllers/previews_controller.rb
===================================================================
--- app/controllers/previews_controller.rb	(revision 17016)
+++ app/controllers/previews_controller.rb	(working copy)
@@ -41,6 +41,11 @@
     render :partial => 'common/preview'
   end
 
+  def comment
+    @text = params[:comment][:comments]
+    render partial: 'common/preview'
+  end
+
   private
 
   def find_project
Index: app/views/news/show.html.erb
===================================================================
--- app/views/news/show.html.erb	(revision 17016)
+++ app/views/news/show.html.erb	(working copy)
@@ -58,8 +58,12 @@
     <%= text_area 'comment', 'comments', :cols => 80, :rows => 15, :class => 'wiki-edit' %>
     <%= wikitoolbar_for 'comment_comments' %>
 </div>
-<p><%= submit_tag l(:button_add) %></p>
+<p>
+  <%= submit_tag l(:button_add) %>
+  <%= preview_link preview_comment_path(project_id: @project), 'add_comment_form', 'comment-preview' %>
+</p>
 <% end %>
+<div id="comment-preview" class="wiki"></div>
 <% end %>
 
 <% html_title @news.title -%>
Index: config/routes.rb
===================================================================
--- config/routes.rb	(revision 17016)
+++ config/routes.rb	(working copy)
@@ -29,6 +29,7 @@
   match '/issues/preview/new/:project_id', :to => 'previews#issue', :as => 'preview_new_issue', :via => [:get, :post, :put, :patch]
   match '/issues/preview/edit/:id', :to => 'previews#issue', :as => 'preview_edit_issue', :via => [:get, :post, :put, :patch]
   match '/issues/preview', :to => 'previews#issue', :as => 'preview_issue', :via => [:get, :post, :put, :patch]
+  match '/comments/preview', to: 'previews#comment', as: 'preview_comment', via: [:post]
 
   match 'projects/:id/wiki', :to => 'wikis#edit', :via => :post
   match 'projects/:id/wiki/destroy', :to => 'wikis#destroy', :via => [:get, :post]
Index: test/functional/previews_controller_test.rb
===================================================================
--- test/functional/previews_controller_test.rb	(revision 17016)
+++ test/functional/previews_controller_test.rb	(working copy)
@@ -141,4 +141,15 @@
     assert_response :success
     assert_select 'fieldset.preview', :text => /News description/
   end
+
+  def test_preview_comment
+    post :comment, params: {
+        project_id: 1,
+        comment: {
+            comments: 'Comment content :)'
+        }
+    }
+    assert_response :success
+    assert_select 'fieldset.preview', text: /Comment content :\)/
+  end
 end
Index: test/integration/routing/previews_test.rb
===================================================================
--- test/integration/routing/previews_test.rb	(revision 17016)
+++ test/integration/routing/previews_test.rb	(working copy)
@@ -28,5 +28,7 @@
     should_route 'POST /issues/preview/edit/321' => 'previews#issue', :id => '321'
 
     should_route 'GET /news/preview' => 'previews#news'
+
+    should_route 'POST /comments/preview' => 'previews#comment'
   end
 end