Follow up: Fixed race condtion while importing history types for the first time.

lib/import/otrs/history.rb

@@ -25,11 +25,22 @@ module Import
       def ensure_history_attribute
         history_attribute = @history_attributes[:history_attribute]
         return if !history_attribute
-        @@created_history_attributes ||= {}
+        return if history_attribute_exists?(history_attribute)
-        return if @@created_history_attributes[history_attribute]
         @@created_history_attributes[history_attribute] = true
         ::History.attribute_lookup(history_attribute)
       end
+
+      def history_attribute_exists?(name)
+        @@created_history_attributes ||= {}
+        return false if !@@created_history_attributes[name]
+
+        # make sure the history attribute is added before we
+        # we perform further import
+        # otherwise the following import logic (add) will
+        # try to add the history attribute, too
+        sleep 1 until ::History::Attribute.find_by(name: name)
+        true
+      end
     end
   end
 end

spec/import/otrs/history_examples.rb

@@ -12,7 +12,8 @@ end
 
 RSpec.shared_examples 'Import::OTRS::History' do
   it 'responds to init_callback' do
-    expect(History).to receive(:add)
+    expect(::History).to receive(:add)
+    allow(::History::Attribute).to receive(:find_by).and_return(true)
     blank_instance = described_class.new({})
     expect(blank_instance).to respond_to('init_callback')
   end