diff --git a/app/controllers/concerns/submission_parameters.rb b/app/controllers/concerns/submission_parameters.rb
index 3a4154d6..1def6759 100644
--- a/app/controllers/concerns/submission_parameters.rb
+++ b/app/controllers/concerns/submission_parameters.rb
@@ -14,14 +14,10 @@ module SubmissionParameters
   private :submission_params
 
   def merge_user(params)
-    if current_user
-      current_user_id = current_user.id
-      current_user_class_name = current_user.class.name
-    end
     # The study_group_id might not be present in the session (e.g. for internal users), resulting in session[:study_group_id] = nil which is intended.
     params.merge(
-      user_id: current_user_id,
-      user_type: current_user_class_name,
+      user_id: current_user.id,
+      user_type: current_user.class.name,
       study_group_id: session[:study_group_id]
     )
   end
diff --git a/app/controllers/exercises_controller.rb b/app/controllers/exercises_controller.rb
index 56a9f6b3..b26ee75b 100644
--- a/app/controllers/exercises_controller.rb
+++ b/app/controllers/exercises_controller.rb
@@ -500,8 +500,7 @@ class ExercisesController < ApplicationController
   def submit
     @submission = Submission.create(submission_params)
     score_submission(@submission)
-    current_user = ExternalUser.find(@submission.user_id)
-    if !current_user.nil? && lti_outcome_service?(@submission.exercise_id, current_user.id)
+    if @submission.user.external_user? && lti_outcome_service?(@submission.exercise_id, @submission.user.id)
       transmit_lti_score
     else
       redirect_after_submit
diff --git a/config/database.yml.ci b/config/database.yml.ci
index 8a62703f..4b898269 100644
--- a/config/database.yml.ci
+++ b/config/database.yml.ci
@@ -5,3 +5,4 @@ test:
   host: localhost
   username: postgres
   password: postgres
+  reaping_frequency: 0
diff --git a/config/initializers/new_framework_defaults_6_0.rb b/config/initializers/new_framework_defaults_6_0.rb
new file mode 100644
index 00000000..0c410fe9
--- /dev/null
+++ b/config/initializers/new_framework_defaults_6_0.rb
@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+# Be sure to restart your server when you modify this file.
+#
+# This file contains migration options to ease your Rails 6.0 upgrade.
+#
+# Once upgraded flip defaults one by one to migrate to the new default.
+#
+# Read the Guide for Upgrading Ruby on Rails for more info on each option.
+
+# Don't force requests from old versions of IE to be UTF-8 encoded.
+# Rails.application.config.action_view.default_enforce_utf8 = false
+
+# Embed purpose and expiry metadata inside signed and encrypted
+# cookies for increased security.
+#
+# This option is not backwards compatible with earlier Rails versions.
+# It's best enabled when your entire app is migrated and stable on 6.0.
+# Rails.application.config.action_dispatch.use_cookies_with_metadata = true
+
+# Change the return value of `ActionDispatch::Response#content_type` to Content-Type header without modification.
+# Rails.application.config.action_dispatch.return_only_media_type_on_content_type = false
+
+# Return false instead of self when enqueuing is aborted from a callback.
+# Rails.application.config.active_job.return_false_on_aborted_enqueue = true
+
+# Send Active Storage analysis and purge jobs to dedicated queues.
+# Rails.application.config.active_storage.queues.analysis = :active_storage_analysis
+# Rails.application.config.active_storage.queues.purge    = :active_storage_purge
+
+# When assigning to a collection of attachments declared via `has_many_attached`, replace existing
+# attachments instead of appending. Use #attach to add new attachments without replacing existing ones.
+# Rails.application.config.active_storage.replace_on_assign_to_many = true
+
+# Use ActionMailer::MailDeliveryJob for sending parameterized and normal mail.
+#
+# The default delivery jobs (ActionMailer::Parameterized::DeliveryJob, ActionMailer::DeliveryJob),
+# will be removed in Rails 6.1. This setting is not backwards compatible with earlier Rails versions.
+# If you send mail in the background, job workers need to have a copy of
+# MailDeliveryJob to ensure all delivery jobs are processed properly.
+# Make sure your entire app is migrated and stable on 6.0 before using this setting.
+# Rails.application.config.action_mailer.delivery_job = "ActionMailer::MailDeliveryJob"
+
+# Enable the same cache key to be reused when the object being cached of type
+# `ActiveRecord::Relation` changes by moving the volatile information (max updated at and count)
+# of the relation's cache key into the cache version to support recycling cache key.
+# Rails.application.config.active_record.collection_cache_versioning = true
diff --git a/spec/controllers/code_ocean/files_controller_spec.rb b/spec/controllers/code_ocean/files_controller_spec.rb
index bca4daaf..7525c097 100644
--- a/spec/controllers/code_ocean/files_controller_spec.rb
+++ b/spec/controllers/code_ocean/files_controller_spec.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'rails_helper'
 
 describe CodeOcean::FilesController do
@@ -48,6 +50,8 @@ describe CodeOcean::FilesController do
       expect { perform_request.call }.to change(CodeOcean::File, :count).by(-1)
     end
 
-    expect_redirect(:exercise)
+    it 'redirects to exercise path' do
+      expect(controller).to redirect_to(exercise)
+    end
   end
 end
diff --git a/spec/controllers/exercises_controller_spec.rb b/spec/controllers/exercises_controller_spec.rb
index 9d77ed24..afb620aa 100644
--- a/spec/controllers/exercises_controller_spec.rb
+++ b/spec/controllers/exercises_controller_spec.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'rails_helper'
 
 describe ExercisesController do
@@ -230,8 +232,8 @@ describe ExercisesController do
   describe 'POST #submit' do
     let(:output) { {} }
     let(:perform_request) { post :submit, format: :json, params: { id: exercise.id, submission: {cause: 'submit', exercise_id: exercise.id} } }
-    let!(:external_user) { FactoryBot.create(:external_user) }
-    let!(:lti_parameter) { FactoryBot.create(:lti_parameter, external_user: external_user, exercise: exercise) }
+    let(:user) { FactoryBot.create(:external_user) }
+    let!(:lti_parameter) { FactoryBot.create(:lti_parameter, external_user: user, exercise: exercise) }
 
     before(:each) do
       allow_any_instance_of(Submission).to receive(:normalized_score).and_return(1)
diff --git a/spec/support/database_cleaner.rb b/spec/support/database_cleaner.rb
index a15f37ff..e283ef43 100644
--- a/spec/support/database_cleaner.rb
+++ b/spec/support/database_cleaner.rb
@@ -1,10 +1,48 @@
+# frozen_string_literal: true
+
+require 'capybara/rspec'
+
 RSpec.configure do |config|
+
+  config.use_transactional_fixtures = false
+
   config.before(:suite) do
-    DatabaseCleaner.strategy = :truncation
+    if config.use_transactional_fixtures?
+      raise(<<-MSG)
+        Delete line `config.use_transactional_fixtures = true` from rails_helper.rb
+        (or set it to false) to prevent uncommitted transactions being used in
+        JavaScript-dependent specs.
+
+        During testing, the app-under-test that the browser driver connects to
+        uses a different database connection to the database connection used by
+        the spec. The app's database connection would not be able to access
+        uncommitted transaction data setup over the spec's database connection.
+      MSG
+    end
+
     DatabaseCleaner.clean_with(:truncation)
   end
 
-  config.around(:each) do |example|
-    DatabaseCleaner.cleaning { example.run }
+  config.before do
+    DatabaseCleaner.strategy = :transaction
+  end
+
+  config.before(:each, type: :feature) do
+    # :rack_test driver's Rack app under test shares database connection
+    # with the specs, so continue to use transaction strategy for speed.
+    unless Capybara.current_driver == :rack_test
+      # Driver is probably for an external browser with an app
+      # under test that does *not* share a database connection with the
+      # specs, so use truncation strategy.
+      DatabaseCleaner.strategy = :truncation
+    end
+  end
+
+  config.before do
+    DatabaseCleaner.start
+  end
+
+  config.append_after do
+    DatabaseCleaner.clean
   end
 end