Add spec for post_page_title for reshares

spec/helpers/posts_helper_spec.rb

@@ -17,6 +17,13 @@ describe PostsHelper, :type => :helper do
         post_page_title(post)
       end
     end
+
+    context "with a reshare" do
+      it "returns 'Reshare by...'" do
+        reshare = FactoryGirl.create(:reshare, author: alice.person)
+        expect(post_page_title(reshare)).to eq I18n.t("posts.show.reshare_by", author: reshare.author_name)
+      end
+    end
   end