diff --git a/.travis.yml b/.travis.yml
index 6d533916..90fd5471 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -12,14 +12,11 @@ addons:
 before_install:
   - export DISPLAY=:99.0
   - sh -e /etc/init.d/xvfb start
-#  Config to run docker tests - doesn't work so far
-#  - sudo apt-get update
-#  - sudo apt-get upgrade lxc-docker
-#  - echo 'DOCKER_OPTS="-H tcp://127.0.0.1:4243 -H unix:///var/run/docker.sock --iptables=false"' | sudo tee /etc/default/docker > /dev/null
-#  - export DOCKER_HOST=tcp://192.168.23.75:2375
-#  - sudo service docker restart
-#  - sleep 5
-#  - docker pull openhpi/docker_ruby
+  - echo 'DOCKER_OPTS="-H tcp://127.0.0.1:2376 -H unix:///var/run/docker.sock --iptables=false"' | sudo tee /etc/default/docker > /dev/null
+  - sudo service docker restart
+  - sleep 5
+  - docker pull openhpi/co_execenv_python
+  - docker pull openhpi/co_execenv_java
 
 before_script:
   - cp .rspec.travis .rspec
@@ -27,6 +24,7 @@ before_script:
   - cp config/code_ocean.yml.travis config/code_ocean.yml
   - cp config/database.yml.travis config/database.yml
   - cp config/secrets.yml.travis config/secrets.yml
+  - cp config/docker.yml.erb.travis config/docker.yml.erb
   - psql --command='CREATE DATABASE travis_ci_test;' --username=postgres
   - bundle exec rake db:schema:load RAILS_ENV=test
 
@@ -35,8 +33,4 @@ language: ruby
 rvm:
 - 2.3.6
   
-script: bundle exec rspec --color --format documentation --require spec_helper --require rails_helper --tag ~docker && bundle exec codeclimate-test-reporter
-# one of the solutions I've found
-#  - sudo docker run --rm=true -v `pwd`:/ansible-apache:rw weldpua2008/docker-ansible:${OS_TYPE}${OS_VERSION}_v${ANSIBLE_VERSION} /bin/bash -c "/ansible-apache/tests/test-in-docker-image.sh ${OS_TYPE} ${OS_VERSION} ${ANSIBLE_VERSION}"
-
-
+script: bundle exec rspec --color --format documentation --require spec_helper --require rails_helper && bundle exec codeclimate-test-reporter
diff --git a/app/models/execution_environment.rb b/app/models/execution_environment.rb
index 74177173..9cd23a48 100644
--- a/app/models/execution_environment.rb
+++ b/app/models/execution_environment.rb
@@ -47,7 +47,7 @@ class ExecutionEnvironment < ActiveRecord::Base
   private :validate_docker_image?
 
   def working_docker_image?
-    DockerClient.pull(docker_image) unless DockerClient.image_tags.include?(docker_image)
+    DockerClient.pull(docker_image) unless DockerClient.find_image_by_tag(docker_image).blank?
     output = DockerClient.new(execution_environment: self).execute_arbitrary_command(VALIDATION_COMMAND)
     errors.add(:docker_image, "error: #{output[:stderr]}") if output[:stderr].present?
   rescue DockerClient::Error => error
diff --git a/config/docker.yml.erb.example b/config/docker.yml.erb.example
index 9f55d126..eb1af61e 100644
--- a/config/docker.yml.erb.example
+++ b/config/docker.yml.erb.example
@@ -34,7 +34,21 @@ production:
   ws_host: ws://localhost:4243 #url to connect rails server to docker host
   ws_client_protocol: wss:// #set the websocket protocol to be used by the client to connect to the rails server (ws on development, wss on production)
 
+staging:
+  <<: *default
+  host: unix:///var/run/docker.sock
+  pool:
+    active: true
+    refill:
+      async: false
+      batch_size: 8
+      interval: 15
+      timeout: 60
+  workspace_root: <%= Rails.root.join('tmp', 'files', Rails.env) %>
+  ws_host: ws://localhost:4243 #url to connect rails server to docker host
+  ws_client_protocol: 'wss:' #set the websocket protocol to be used by the client to connect to the rails server (ws on development, wss on production)
+
 test:
   <<: *default
-  host: tcp://192.168.59.104:2376
+  host: tcp://127.0.0.1:2376
   workspace_root: <%= File.join('/', 'shared', Rails.env) %>
diff --git a/config/docker.yml.erb b/config/docker.yml.erb.travis
similarity index 94%
rename from config/docker.yml.erb
rename to config/docker.yml.erb.travis
index c1871de7..eb1af61e 100644
--- a/config/docker.yml.erb
+++ b/config/docker.yml.erb.travis
@@ -32,7 +32,7 @@ production:
       timeout: 60
   workspace_root: <%= Rails.root.join('tmp', 'files', Rails.env) %>
   ws_host: ws://localhost:4243 #url to connect rails server to docker host
-  ws_client_protocol: 'wss:' #set the websocket protocol to be used by the client to connect to the rails server (ws on development, wss on production)
+  ws_client_protocol: wss:// #set the websocket protocol to be used by the client to connect to the rails server (ws on development, wss on production)
 
 staging:
   <<: *default
@@ -50,5 +50,5 @@ staging:
 
 test:
   <<: *default
-  host: tcp://192.168.59.104:2376
+  host: tcp://127.0.0.1:2376
   workspace_root: <%= File.join('/', 'shared', Rails.env) %>
diff --git a/public/uploads/files/4/chai.ogg b/public/uploads/files/4/chai.ogg
deleted file mode 100644
index 86190d0c..00000000
Binary files a/public/uploads/files/4/chai.ogg and /dev/null differ
diff --git a/public/uploads/files/5/devstories.mp4 b/public/uploads/files/5/devstories.mp4
deleted file mode 100644
index 9e7d328d..00000000
Binary files a/public/uploads/files/5/devstories.mp4 and /dev/null differ
diff --git a/public/uploads/files/6/devstories.webm b/public/uploads/files/6/devstories.webm
deleted file mode 100644
index 84fff0ed..00000000
Binary files a/public/uploads/files/6/devstories.webm and /dev/null differ
diff --git a/public/uploads/files/7/poster.png b/public/uploads/files/7/poster.png
deleted file mode 100644
index d950cef4..00000000
Binary files a/public/uploads/files/7/poster.png and /dev/null differ
diff --git a/spec/concerns/lti_spec.rb b/spec/concerns/lti_spec.rb
index a7b1dfcc..4fb8dc5f 100644
--- a/spec/concerns/lti_spec.rb
+++ b/spec/concerns/lti_spec.rb
@@ -98,7 +98,7 @@ describe Lti do
     let(:consumer) { FactoryBot.create(:consumer) }
     let(:score) { 0.5 }
     let(:submission) { FactoryBot.create(:submission) }
-    let!(:lti_parameter) { FactoryBot.create(:lti_parameter)}
+    let!(:lti_parameter) { FactoryBot.create(:lti_parameter, consumers_id: consumer.id, external_users_id: submission.user_id, exercises_id: submission.exercise_id)}
 
     context 'with an invalid score' do
       it 'raises an exception' do
@@ -114,7 +114,6 @@ describe Lti do
 
         context 'when grading is not supported' do
           it 'returns a corresponding status' do
-            skip('ralf: this does not work, since send_score pulls data from the database, which then returns an empty array. On this is called .first, which returns nil and lets the test fail. Before Toms changes, this was taken from the session, which could be mocked')
             expect_any_instance_of(IMS::LTI::ToolProvider).to receive(:outcome_service?).and_return(false)
             expect(controller.send(:send_score, submission.exercise_id, score, submission.user_id)[:status]).to eq('unsupported')
           end
@@ -133,12 +132,10 @@ describe Lti do
           end
 
           it 'sends the score' do
-            skip('ralf: this does not work, since send_score pulls data from the database, which then returns an empty array. On this is called .first, which returns nil and lets the test fail. Before Toms changes, this was taken from the session, which could be mocked')
             controller.send(:send_score, submission.exercise_id, score, submission.user_id)
           end
 
           it 'returns code, message, and status' do
-            skip('ralf: this does not work, since send_score pulls data from the database, which then returns an empty array. On this is called .first, which returns nil and lets the test fail. Before Toms changes, this was taken from the session, which could be mocked')
             result = controller.send(:send_score, submission.exercise_id, score, submission.user_id)
             expect(result[:code]).to eq(response.response_code)
             expect(result[:message]).to eq(response.body)
diff --git a/spec/factories/user_exercise_feedback.rb b/spec/factories/user_exercise_feedback.rb
index 42c5d803..3c43158f 100644
--- a/spec/factories/user_exercise_feedback.rb
+++ b/spec/factories/user_exercise_feedback.rb
@@ -2,6 +2,7 @@ FactoryBot.define do
   factory :user_exercise_feedback, class: UserExerciseFeedback do
     created_by_external_user
     feedback_text 'Most suitable exercise ever'
+    association :exercise, factory: :math
   end
 
 end
diff --git a/spec/lib/docker_client_spec.rb b/spec/lib/docker_client_spec.rb
index 5901c130..5d1118bd 100644
--- a/spec/lib/docker_client_spec.rb
+++ b/spec/lib/docker_client_spec.rb
@@ -2,12 +2,22 @@ require 'rails_helper'
 require 'seeds_helper'
 
 describe DockerClient, docker: true do
+  WORKSPACE_PATH = '/tmp/code_ocean_test'
+
   let(:command) { 'whoami' }
   let(:docker_client) { described_class.new(execution_environment: FactoryBot.build(:java), user: FactoryBot.build(:admin)) }
   let(:execution_environment) { FactoryBot.build(:java) }
   let(:image) { double }
   let(:submission) { FactoryBot.create(:submission) }
-  let(:workspace_path) { '/tmp' }
+  let(:workspace_path) { WORKSPACE_PATH }
+
+  before(:all) do
+    FileUtils.mkdir_p(WORKSPACE_PATH)
+  end
+
+  after(:all) do
+    FileUtils.rm_rf(WORKSPACE_PATH)
+  end
 
   describe '.check_availability!' do
     context 'when a socket error occurs' do
@@ -129,7 +139,7 @@ describe DockerClient, docker: true do
     after(:each) { docker_client.send(:create_workspace_files, container, submission) }
 
     it 'creates submission-specific directories' do
-      expect(Dir).to receive(:mkdir).at_least(:once)
+      expect(Dir).to receive(:mkdir).at_least(:once).and_call_original
     end
 
     it 'copies binary files' do
diff --git a/test/factories/error_template_attributes.rb b/test/factories/error_template_attributes.rb
index 84e65757..2e867ec5 100644
--- a/test/factories/error_template_attributes.rb
+++ b/test/factories/error_template_attributes.rb
@@ -1,6 +1,5 @@
 FactoryBot.define do
   factory :error_template_attribute do
-    error_template nil
     key "MyString"
     regex "MyString"
   end