sort by content if no course modules exist

closes CNVS-23800

test plan
- export a course with no modules
- create an ePub, which would normally result in module sorting by default
- the generated ePub should be sorted by content

Change-Id: I2e49b7cffd4c3f4bef12357c24814a0c0f837c9d
Reviewed-on: https://gerrit.instructure.com/64665
QA-Review: Deepeeca Soundarrajan <dsoundarrajan@instructure.com>
Product-Review: Cosme Salazar <cosme@instructure.com>
Tested-by: Jenkins
Reviewed-by: John Corrigan <jcorrigan@instructure.com>

Author: MLBerns

lib/cc/exporter/epub/exporter.rb

@@ -19,7 +19,7 @@ class Exporter
 
     def initialize(cartridge, sort_by_content=false)
       @cartridge = cartridge
-      @sort_by_content = sort_by_content
+      @sort_by_content = sort_by_content || cartridge_json[:modules].empty?
     end
     attr_reader :cartridge, :sort_by_content
 

spec/fixtures/exporter/cc-with-modules-export.imscc

@@ -6,14 +6,25 @@
 
   before(:once) do
     def cartridge_path
-      File.join(File.dirname(__FILE__), "/../../../../fixtures/migration/unicode-filename-test-export.imscc")
+      File.join(File.dirname(__FILE__), "/../../../../fixtures/exporter/cc-with-modules-export.imscc")
+    end
+
+    def cartridge_without_modules_path
+      File.join(File.dirname(__FILE__), "/../../../../fixtures/exporter/cc-without-modules-export.imscc")
     end
 
     @attachment = Attachment.create({
       context: course,
       filename: 'exortable-test-file',
       uploaded_data: File.open(cartridge_path)
     })
+
+    @attachment_without_modules = Attachment.create({
+      context: course,
+      filename: 'exortable-test-file',
+      uploaded_data: File.open(cartridge_without_modules_path)
+    })
+
   end
 
   context "create ePub default settings" do
@@ -30,6 +41,16 @@ def cartridge_path
     end
   end
 
+  context "default settings with no modules present" do
+    let(:exporter) do
+      CC::Exporter::Epub::Exporter.new(@attachment_without_modules.open)
+    end
+
+    it "should fall back to sorting by content type" do
+      expect(exporter.templates.key?(:modules)).to be_falsey
+    end
+  end
+
   context "create ePub with content type sorting" do
     let(:exporter) do
       CC::Exporter::Epub::Exporter.new(@attachment.open, true)