collections: add rdcp sort test re: user select

- Only apply RDCP sorting if a user has not already selected a sort
  option in the UI
- Adds a test for a user selected option when browsing RDCP collections

app/controllers/catalog_controller.rb

@@ -305,12 +305,15 @@ def collection_search
       @current_unit_code = params[:id]
     end
 
-    # sort by title
-    params[:sort] = 'title_ssi asc' unless params[:sort]
+    # apply default sorting rules if user has not selected one
+    unless params[:sort]
+      # sort by title
+      params[:sort] = 'title_ssi asc'
+      # RDCP prefers their collections sorted by most recently created first
+      # Therefore, we're sorting by modified date rather than title
+      params[:sort] = 'system_modified_dtsi desc, title_ssi asc' if params[:id].eql? 'rdcp'
+    end
 
-    # RDCP prefers their collections sorted by most recently created first
-    # Therefore, we're sorting by modified date rather than title
-    params[:sort] = 'system_modified_dtsi desc, title_ssi asc' if params[:id].eql? 'rdcp'
     (@response, @document_list) = get_search_results params, params
 
     # update session

spec/features/collections_search.rb

@@ -20,12 +20,19 @@
       @oldest_collection.delete
       @newest_collection.delete
     end
-    it 'should sort by most recent collection, descending to oldest' do
+    it 'should sort by most recent collection by default, descending to oldest' do
       visit dams_unit_collections_path('rdcp')
       old_collection_sort_order = page.body.index('A Old Collection')
       new_collection_sort_order = page.body.index('The New Collection')
       expect(old_collection_sort_order).to be > new_collection_sort_order
     end
+
+    it 'should still allow user selected sort options' do
+      visit dams_unit_collections_path('rdcp', { sort: 'title_ssi asc' })
+      old_collection_sort_order = page.body.index('A Old Collection')
+      new_collection_sort_order = page.body.index('The New Collection')
+      expect(old_collection_sort_order).to be < new_collection_sort_order
+    end
   end
 
   describe 'DLDP browse by collection page' do