rails 5: simplify attachment transaction callbacks

refs CNVS-34862

in rails 5, we can't detect a transaction that was elided in favor
of joining a parent transaction, so don't try to. instead, always
call attachment callbacks immediately in the transaction, except
for the one spec that's actually testing that we don't do it in
a transaction

Change-Id: Ia53730586e305d95c41269b3be643194392a141d
Reviewed-on: https://gerrit.instructure.com/103757
Tested-by: Jenkins
Reviewed-by: James Williams  <jamesw@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>

gems/attachment_fu/lib/attachment_fu.rb

@@ -198,32 +198,6 @@ module AttachmentFu # :nodoc:
         tmp.close
       end
     end
-
-    if Rails.env.test?
-      # thanks to test_after_commit, we can use transactional fixtures,
-      # but we still need reach into connection, since we conditionally
-      # use after_transaction_commit based on transaction nesting
-      if CANVAS_RAILS4_2
-        def open_transactions
-          connection.instance_variable_get(:@test_open_transactions)
-        end
-      else
-        # count the number of transactions since the last joinable transaction
-        def open_transactions
-          stack = connection.transaction_manager.instance_variable_get(:@stack)
-          count = 0
-          stack.reverse.each do |transaction|
-            break unless transaction.joinable?
-            count += 1
-          end
-          count
-        end
-      end
-    else
-      def open_transactions
-        connection.open_transactions
-      end
-    end
   end
 
   module InstanceMethods
@@ -567,10 +541,10 @@ module AttachmentFu # :nodoc:
             run_callbacks(:save_and_attachment_processing)
           end
 
-          if self.class.open_transactions == 1 # yes, == 1, not > 0 ... see comment above
-            self.class.connection.after_transaction_commit(&save_and_callbacks)
-          else
+          if Rails.env.test?
             save_and_callbacks.call()
+          else
+            self.class.connection.after_transaction_commit(&save_and_callbacks)
           end
         else
           run_callbacks(:save_and_attachment_processing)

spec/models/attachment_spec.rb

@@ -303,10 +303,11 @@ describe Attachment do
       end
 
       it "should delay upload until the #save transaction is committed" do
+        allow(Rails.env).to receive(:test?).and_return(false)
         @attachment.uploaded_data = default_uploaded_data
-        Attachment.connection.expects(:after_transaction_commit).twice
-        @attachment.expects(:touch_context_if_appropriate).never
-        @attachment.expects(:ensure_media_object).never
+        expect(Attachment.connection).to receive(:after_transaction_commit).twice
+        expect(@attachment).to receive(:touch_context_if_appropriate).never
+        expect(@attachment).to receive(:ensure_media_object).never
         @attachment.save
       end
     end