Convert DorHarvester#resources into an enumerable

app/models/dor_harvester.rb

@@ -11,7 +11,9 @@ def instance(current_exhibit)
   end
 
   def resources
-    @resources ||= druids.map { |d| Spotlight::Dor::Resources.indexer.resource(d) }
+    return to_enum(:resources) { druids.size } unless block_given?
+
+    druids.each { |d| yield Spotlight::Dor::Resources.indexer.resource(d) }
   end
 
   def druids

spec/services/dor_solr_document_builder_spec.rb

@@ -1,14 +1,18 @@
 require 'rails_helper'
 
 describe DorSolrDocumentBuilder do
+  subject { described_class.new harvester }
+
   let(:exhibit) { FactoryGirl.create(:exhibit) }
-  let(:harvester) { DorHarvester.new druid_list: 'xf680rd3068', exhibit: exhibit }
-  let(:resource) { harvester.resources.first }
+  let(:druid) { 'xf680rd3068' }
+  let(:harvester) { DorHarvester.new druid_list: druid, exhibit: exhibit }
+  let(:resources) { [resource].to_enum }
+  let(:resource) { Harvestdor::Indexer::Resource.new(indexer, druid) }
   let(:indexer) { Spotlight::Dor::Resources.indexer }
 
-  subject { described_class.new harvester }
-
   before do
+    allow(resource).to receive(:exists?).and_return(true)
+    allow(harvester).to receive(:resources).and_return(resources)
     allow(harvester).to receive(:blacklight_solr).and_return(double)
     allow(harvester).to receive(:to_global_id).and_return('x')
     allow(indexer).to receive(:solr_document)