use page title as fallback if preview can't be parsed

Author: nathanstitt

app/subsystems/tasks/models/tasked_reading.rb

@@ -16,8 +16,7 @@ def has_learning_objectives?
   end
 
   def content_preview
-    text = document_title.presence || data_title.presence || class_title.presence
-    text || "Reading Step ##{id}"
+    document_title.presence || data_title.presence || class_title.presence || task_step.page.title
   end
 
   private

spec/subsystems/tasks/models/tasked_reading_spec.rb

@@ -9,7 +9,6 @@
   it { is_expected.to validate_presence_of(:content) }
 
   describe '#content_preview' do
-    let(:default_reading_copy) { "Reading Step ##{tasked_reading.id}" }
 
     before do
       tasked_reading.content = content
@@ -77,8 +76,8 @@
         HTML
       end
 
-      it "defaults to an expected copy" do
-        expect(tasked_reading.content_preview).to eq(default_reading_copy)
+      it "defaults to page title" do
+        expect(tasked_reading.content_preview).to eq(tasked_reading.task_step.page.title)
       end
     end
   end