diff --git a/spec/factories/code_ocean/file.rb b/spec/factories/code_ocean/file.rb
index 64245e97..61241593 100644
--- a/spec/factories/code_ocean/file.rb
+++ b/spec/factories/code_ocean/file.rb
@@ -2,7 +2,7 @@ require 'seeds_helper'
 
 module CodeOcean
   FactoryBot.define do
-    factory :file, class: CodeOcean::File do
+    factory :file, class: 'CodeOcean::File' do
       content { '' }
       association :context, factory: :submission
       association :file_type, factory: :dot_rb
@@ -18,7 +18,7 @@ module CodeOcean
       end
     end
 
-    factory :test_file, class: CodeOcean::File do
+    factory :test_file, class: 'CodeOcean::File' do
       content { '' }
       association :context, factory: :dummy
       association :file_type, factory: :dot_rb
diff --git a/spec/factories/execution_environment.rb b/spec/factories/execution_environment.rb
index 7eaaa49b..3961441a 100644
--- a/spec/factories/execution_environment.rb
+++ b/spec/factories/execution_environment.rb
@@ -1,5 +1,5 @@
 FactoryBot.define do
-  factory :coffee_script, class: ExecutionEnvironment do
+  factory :coffee_script, class: 'ExecutionEnvironment' do
     created_by_teacher
     default_memory_limit
     docker_image { 'hklement/ubuntu-coffee:latest' }
@@ -13,7 +13,7 @@ FactoryBot.define do
     singleton_execution_environment
   end
 
-  factory :html, class: ExecutionEnvironment do
+  factory :html, class: 'ExecutionEnvironment' do
     created_by_teacher
     default_memory_limit
     docker_image { 'hklement/ubuntu-html:latest' }
@@ -29,7 +29,7 @@ FactoryBot.define do
     testing_framework { 'RspecAdapter' }
   end
 
-  factory :java, class: ExecutionEnvironment do
+  factory :java, class: 'ExecutionEnvironment' do
     created_by_teacher
     default_memory_limit
     docker_image { 'openhpi/co_execenv_java:latest' }
@@ -45,7 +45,7 @@ FactoryBot.define do
     testing_framework { 'JunitAdapter' }
   end
 
-  factory :jruby, class: ExecutionEnvironment do
+  factory :jruby, class: 'ExecutionEnvironment' do
     created_by_teacher
     default_memory_limit
     docker_image { 'hklement/ubuntu-jruby:latest' }
@@ -61,7 +61,7 @@ FactoryBot.define do
     testing_framework { 'RspecAdapter' }
   end
 
-  factory :node_js, class: ExecutionEnvironment do
+  factory :node_js, class: 'ExecutionEnvironment' do
     created_by_teacher
     default_memory_limit
     docker_image { 'hklement/ubuntu-node:latest' }
@@ -75,7 +75,7 @@ FactoryBot.define do
     singleton_execution_environment
   end
 
-  factory :python, class: ExecutionEnvironment do
+  factory :python, class: 'ExecutionEnvironment' do
     created_by_teacher
     default_memory_limit
     docker_image { 'openhpi/co_execenv_python:latest' }
@@ -91,7 +91,7 @@ FactoryBot.define do
     testing_framework { 'PyUnitAdapter' }
   end
 
-  factory :ruby, class: ExecutionEnvironment do
+  factory :ruby, class: 'ExecutionEnvironment' do
     created_by_teacher
     default_memory_limit
     docker_image { 'hklement/ubuntu-ruby:latest' }
@@ -107,7 +107,7 @@ FactoryBot.define do
     testing_framework { 'RspecAdapter' }
   end
 
-  factory :sinatra, class: ExecutionEnvironment do
+  factory :sinatra, class: 'ExecutionEnvironment' do
     created_by_teacher
     default_memory_limit
     docker_image { 'hklement/ubuntu-sinatra:latest' }
@@ -124,7 +124,7 @@ FactoryBot.define do
     testing_framework { 'RspecAdapter' }
   end
 
-  factory :sqlite, class: ExecutionEnvironment do
+  factory :sqlite, class: 'ExecutionEnvironment' do
     created_by_teacher
     default_memory_limit
     docker_image { 'hklement/ubuntu-sqlite:latest' }
diff --git a/spec/factories/exercise.rb b/spec/factories/exercise.rb
index 92ed180f..931e6e51 100644
--- a/spec/factories/exercise.rb
+++ b/spec/factories/exercise.rb
@@ -14,7 +14,7 @@ def create_seed_file(exercise, path, file_attributes = {})
 end
 
 FactoryBot.define do
-  factory :audio_video, class: Exercise do
+  factory :audio_video, class: 'Exercise' do
     created_by_teacher
     description { "Try HTML's audio and video capabilities." }
     association :execution_environment, factory: :html
@@ -32,7 +32,7 @@ FactoryBot.define do
     end
   end
 
-  factory :dummy, class: Exercise do
+  factory :dummy, class: 'Exercise' do
     created_by_teacher
     description { 'Dummy' }
     association :execution_environment, factory: :ruby
@@ -58,7 +58,7 @@ FactoryBot.define do
 
   end
 
-  factory :even_odd, class: Exercise do
+  factory :even_odd, class: 'Exercise' do
     created_by_teacher
     description { 'Implement two methods even and odd which return whether a given number is even or odd, respectively.' }
     association :execution_environment, factory: :python
@@ -72,7 +72,7 @@ FactoryBot.define do
     end
   end
 
-  factory :fibonacci, class: Exercise do
+  factory :fibonacci, class: 'Exercise' do
     created_by_teacher
     description { 'Implement a recursive function that calculates a requested Fibonacci number.' }
     association :execution_environment, factory: :ruby
@@ -88,7 +88,7 @@ FactoryBot.define do
     end
   end
 
-  factory :files, class: Exercise do
+  factory :files, class: 'Exercise' do
     created_by_teacher
     description { 'Learn how to work with files.' }
     association :execution_environment, factory: :ruby
@@ -102,7 +102,7 @@ FactoryBot.define do
     end
   end
 
-  factory :geolocation, class: Exercise do
+  factory :geolocation, class: 'Exercise' do
     created_by_teacher
     description { "Use the HTML5 Geolocation API to get the user's geographical position." }
     association :execution_environment, factory: :html
@@ -115,7 +115,7 @@ FactoryBot.define do
     end
   end
 
-  factory :hello_world, class: Exercise do
+  factory :hello_world, class: 'Exercise' do
     created_by_teacher
     description { "Write a simple 'Hello World' application." }
     association :execution_environment, factory: :ruby
@@ -128,7 +128,7 @@ FactoryBot.define do
     end
   end
 
-  factory :math, class: Exercise do
+  factory :math, class: 'Exercise' do
     created_by_teacher
     description { 'Implement a recursive math library.' }
     association :execution_environment, factory: :java
@@ -143,7 +143,7 @@ FactoryBot.define do
     end
   end
 
-  factory :primes, class: Exercise do
+  factory :primes, class: 'Exercise' do
     created_by_teacher
     description { 'Write a function that prints the first n prime numbers.' }
     association :execution_environment, factory: :node_js
@@ -155,7 +155,7 @@ FactoryBot.define do
     end
   end
 
-  factory :sql_select, class: Exercise do
+  factory :sql_select, class: 'Exercise' do
     created_by_teacher
     description { 'Learn to use the SELECT statement.' }
     association :execution_environment, factory: :sqlite
@@ -169,7 +169,7 @@ FactoryBot.define do
     end
   end
 
-  factory :tdd, class: Exercise do
+  factory :tdd, class: 'Exercise' do
     created_by_teacher
     description { 'Learn to appreciate test-driven development.' }
     association :execution_environment, factory: :ruby
@@ -182,7 +182,7 @@ FactoryBot.define do
     end
   end
 
-  factory :web_app, class: Exercise do
+  factory :web_app, class: 'Exercise' do
     created_by_teacher
     description { 'Build a simple Web application with Sinatra.' }
     association :execution_environment, factory: :sinatra
diff --git a/spec/factories/file_type.rb b/spec/factories/file_type.rb
index 07ee81bd..f08e3b73 100644
--- a/spec/factories/file_type.rb
+++ b/spec/factories/file_type.rb
@@ -1,5 +1,5 @@
 FactoryBot.define do
-  factory :dot_coffee, class: FileType do
+  factory :dot_coffee, class: 'FileType' do
     created_by_admin
     editor_mode { 'ace/mode/coffee' }
     executable
@@ -9,7 +9,7 @@ FactoryBot.define do
     singleton_file_type
   end
 
-  factory :dot_gif, class: FileType do
+  factory :dot_gif, class: 'FileType' do
     binary
     created_by_admin
     file_extension { '.gif' }
@@ -18,7 +18,7 @@ FactoryBot.define do
     singleton_file_type
   end
 
-  factory :dot_html, class: FileType do
+  factory :dot_html, class: 'FileType' do
     created_by_admin
     editor_mode { 'ace/mode/html' }
     file_extension { '.html' }
@@ -28,7 +28,7 @@ FactoryBot.define do
     singleton_file_type
   end
 
-  factory :dot_java, class: FileType do
+  factory :dot_java, class: 'FileType' do
     created_by_admin
     editor_mode { 'ace/mode/java' }
     executable
@@ -38,7 +38,7 @@ FactoryBot.define do
     singleton_file_type
   end
 
-  factory :dot_jpg, class: FileType do
+  factory :dot_jpg, class: 'FileType' do
     binary
     created_by_admin
     file_extension { '.jpg' }
@@ -47,7 +47,7 @@ FactoryBot.define do
     singleton_file_type
   end
 
-  factory :dot_js, class: FileType do
+  factory :dot_js, class: 'FileType' do
     created_by_admin
     editor_mode { 'ace/mode/javascript' }
     executable
@@ -57,7 +57,7 @@ FactoryBot.define do
     singleton_file_type
   end
 
-  factory :dot_json, class: FileType do
+  factory :dot_json, class: 'FileType' do
     created_by_admin
     editor_mode { 'ace/mode/javascript' }
     file_extension { '.json' }
@@ -67,7 +67,7 @@ FactoryBot.define do
     singleton_file_type
   end
 
-  factory :dot_md, class: FileType do
+  factory :dot_md, class: 'FileType' do
     created_by_admin
     editor_mode { 'ace/mode/markdown' }
     file_extension { '.md' }
@@ -76,7 +76,7 @@ FactoryBot.define do
     singleton_file_type
   end
 
-  factory :dot_mp3, class: FileType do
+  factory :dot_mp3, class: 'FileType' do
     binary
     created_by_admin
     file_extension { '.mp3' }
@@ -85,7 +85,7 @@ FactoryBot.define do
     singleton_file_type
   end
 
-  factory :dot_mp4, class: FileType do
+  factory :dot_mp4, class: 'FileType' do
     binary
     created_by_admin
     file_extension { '.mp4' }
@@ -94,7 +94,7 @@ FactoryBot.define do
     singleton_file_type
   end
 
-  factory :dot_ogg, class: FileType do
+  factory :dot_ogg, class: 'FileType' do
     binary
     created_by_admin
     file_extension { '.ogg' }
@@ -103,7 +103,7 @@ FactoryBot.define do
     singleton_file_type
   end
 
-  factory :dot_png, class: FileType do
+  factory :dot_png, class: 'FileType' do
     binary
     created_by_admin
     file_extension { '.png' }
@@ -112,7 +112,7 @@ FactoryBot.define do
     singleton_file_type
   end
 
-  factory :dot_py, class: FileType do
+  factory :dot_py, class: 'FileType' do
     created_by_admin
     editor_mode { 'ace/mode/python' }
     executable
@@ -122,7 +122,7 @@ FactoryBot.define do
     singleton_file_type
   end
 
-  factory :dot_rb, class: FileType do
+  factory :dot_rb, class: 'FileType' do
     created_by_admin
     editor_mode { 'ace/mode/ruby' }
     executable
@@ -132,7 +132,7 @@ FactoryBot.define do
     singleton_file_type
   end
 
-  factory :dot_svg, class: FileType do
+  factory :dot_svg, class: 'FileType' do
     created_by_admin
     editor_mode { 'ace/mode/svg' }
     file_extension { '.svg' }
@@ -142,7 +142,7 @@ FactoryBot.define do
     singleton_file_type
   end
 
-  factory :dot_sql, class: FileType do
+  factory :dot_sql, class: 'FileType' do
     created_by_admin
     editor_mode { 'ace/mode/sql' }
     executable
@@ -152,7 +152,7 @@ FactoryBot.define do
     singleton_file_type
   end
 
-  factory :dot_txt, class: FileType do
+  factory :dot_txt, class: 'FileType' do
     created_by_admin
     editor_mode { 'ace/mode/plain_text' }
     file_extension { '.txt' }
@@ -162,7 +162,7 @@ FactoryBot.define do
     singleton_file_type
   end
 
-  factory :dot_webm, class: FileType do
+  factory :dot_webm, class: 'FileType' do
     binary
     created_by_admin
     file_extension { '.webm' }
@@ -171,7 +171,7 @@ FactoryBot.define do
     singleton_file_type
   end
 
-  factory :dot_xml, class: FileType do
+  factory :dot_xml, class: 'FileType' do
     created_by_admin
     editor_mode { 'ace/mode/xml' }
     file_extension { '.xml' }
@@ -181,7 +181,7 @@ FactoryBot.define do
     singleton_file_type
   end
 
-  factory :makefile, class: FileType do
+  factory :makefile, class: 'FileType' do
     created_by_admin
     editor_mode { 'ace/mode/makefile' }
     executable
diff --git a/spec/factories/internal_user.rb b/spec/factories/internal_user.rb
index 5dec652e..8ef4e63d 100644
--- a/spec/factories/internal_user.rb
+++ b/spec/factories/internal_user.rb
@@ -1,5 +1,5 @@
 FactoryBot.define do
-  factory :admin, class: InternalUser do
+  factory :admin, class: 'InternalUser' do
     activated_user
     association :consumer
     email { 'admin@example.org' }
@@ -9,7 +9,7 @@ FactoryBot.define do
     singleton_internal_user
   end
 
-  factory :teacher, class: InternalUser do
+  factory :teacher, class: 'InternalUser' do
     activated_user
     association :consumer
     generated_email
diff --git a/spec/factories/proxy_exercise.rb b/spec/factories/proxy_exercise.rb
index 3118da81..a100f8d6 100644
--- a/spec/factories/proxy_exercise.rb
+++ b/spec/factories/proxy_exercise.rb
@@ -1,5 +1,5 @@
 FactoryBot.define do
-  factory :proxy_exercise, class: ProxyExercise do
+  factory :proxy_exercise, class: 'ProxyExercise' do
     created_by_teacher
     token { 'dummytoken' }
     title { 'Dummy' }
diff --git a/spec/factories/study_group.rb b/spec/factories/study_group.rb
index 1676eaa0..6256adde 100644
--- a/spec/factories/study_group.rb
+++ b/spec/factories/study_group.rb
@@ -1,5 +1,5 @@
 FactoryBot.define do
-  factory :study_group, class: StudyGroup do
+  factory :study_group, class: 'StudyGroup' do
     association :consumer
     sequence :name do |n|
       "TestGroup#{n}"
diff --git a/spec/factories/user_exercise_feedback.rb b/spec/factories/user_exercise_feedback.rb
index d3a79029..ff0ff763 100644
--- a/spec/factories/user_exercise_feedback.rb
+++ b/spec/factories/user_exercise_feedback.rb
@@ -1,5 +1,5 @@
 FactoryBot.define do
-  factory :user_exercise_feedback, class: UserExerciseFeedback do
+  factory :user_exercise_feedback, class: 'UserExerciseFeedback' do
     created_by_external_user
     feedback_text { 'Most suitable exercise ever' }
     association :exercise, factory: :math