diff --git a/Gemfile b/Gemfile
index f3626183..f980a082 100644
--- a/Gemfile
+++ b/Gemfile
@@ -74,4 +74,5 @@ group :test do
   gem 'rspec-autotest'
   gem 'rspec-rails'
   gem 'simplecov', require: false
+  gem 'webmock'
 end
diff --git a/Gemfile.lock b/Gemfile.lock
index 853a2f87..fb93dbf4 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -128,6 +128,8 @@ GEM
     chronic (0.10.2)
     coderay (1.1.2)
     concurrent-ruby (1.1.5)
+    crack (0.4.3)
+      safe_yaml (~> 1.0.0)
     crass (1.0.5)
     database_cleaner (1.7.0)
     debug_inspector (0.0.3)
@@ -156,6 +158,7 @@ GEM
     forgery (0.7.0)
     globalid (0.4.2)
       activesupport (>= 4.2.0)
+    hashdiff (1.0.0)
     headless (2.3.1)
     highline (2.0.3)
     http-accept (1.7.0)
@@ -348,6 +351,7 @@ GEM
       json (~> 2.1)
       structured_warnings (~> 0.3)
     rubyzip (2.0.0)
+    safe_yaml (1.0.5)
     sass-rails (6.0.0)
       sassc-rails (~> 2.1, >= 2.1.1)
     sassc (2.2.1)
@@ -409,6 +413,10 @@ GEM
       activemodel (>= 5.0)
       bindex (>= 0.4.0)
       railties (>= 5.0)
+    webmock (3.7.6)
+      addressable (>= 2.3.6)
+      crack (>= 0.3.2)
+      hashdiff (>= 0.4.0, < 2.0.0)
     webpacker (4.2.0)
       activesupport (>= 4.2)
       rack-proxy (>= 0.6.1)
@@ -491,6 +499,7 @@ DEPENDENCIES
   turbolinks
   uglifier
   web-console
+  webmock
   webpacker
   whenever
 
diff --git a/app/controllers/codeharbor_links_controller.rb b/app/controllers/codeharbor_links_controller.rb
index 8c25df66..802448f6 100644
--- a/app/controllers/codeharbor_links_controller.rb
+++ b/app/controllers/codeharbor_links_controller.rb
@@ -18,7 +18,7 @@ class CodeharborLinksController < ApplicationController
     @codeharbor_link = CodeharborLink.new(codeharbor_link_params)
     @codeharbor_link.user = current_user
     authorize!
-    create_and_respond(object: @codeharbor_link, path: proc { @codeharbor_link.user })
+    create_and_respond(object: @codeharbor_link, path: -> { @codeharbor_link.user })
   end
 
   def update
diff --git a/app/controllers/exercises_controller.rb b/app/controllers/exercises_controller.rb
index 468d18ac..f0dd0f5a 100644
--- a/app/controllers/exercises_controller.rb
+++ b/app/controllers/exercises_controller.rb
@@ -123,14 +123,13 @@ class ExercisesController < ApplicationController
 
   def export_external_check
     codeharbor_check = ExerciseService::CheckExternal.call(uuid: @exercise.uuid, codeharbor_link: current_user.codeharbor_link)
-
     render json: {
       message: codeharbor_check[:message],
       actions: render_to_string(
         partial: 'export_actions',
         locals: {
           exercise: @exercise,
-          exercise_found: codeharbor_check[:exercise_found],
+          # exercise_found: codeharbor_check[:exercise_found],
           update_right: codeharbor_check[:update_right],
           error: codeharbor_check[:error],
           exported: false
@@ -142,7 +141,7 @@ class ExercisesController < ApplicationController
   def export_external_confirm
     push_type = params[:push_type]
 
-    return render :fail unless %w[create_new export].include? push_type
+    return render json: {}, status: 500 unless %w[create_new export].include? push_type
 
     @exercise.uuid = SecureRandom.uuid if push_type == 'create_new'
 
@@ -195,7 +194,6 @@ class ExercisesController < ApplicationController
   rescue Proforma::ProformaError
     render json: t('exercises.export_codeharbor.export_errors.invalid'), status: 400
   rescue StandardError
-    logger.info(exercise.errors.full_messages)
     render json: t('exercises.export_codeharbor.export_errors.internal_error'), status: 500
   end
 
diff --git a/app/services/exercise_service/check_external.rb b/app/services/exercise_service/check_external.rb
index 1cce7614..1aac945b 100644
--- a/app/services/exercise_service/check_external.rb
+++ b/app/services/exercise_service/check_external.rb
@@ -17,7 +17,7 @@ module ExerciseService
 
       {error: false}.merge(response_hash.slice(:message, :exercise_found, :update_right))
     rescue Faraday::Error => e
-      {error: true, message: t('exercises.export_exercise.error', message: e.message)}
+      {error: true, message: I18n.t('exercises.export_codeharbor.error', message: e.message)}
     end
 
     private
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 76091159..8a0707e1 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -327,7 +327,7 @@ en:
     export_codeharbor:
       label: Export to Codeharbor
       dialogtitle: Export to Codeharbor
-      successfully_exported: 'Exercise has successfully been exported.<br>ID: %{id}<br>Title: %{title}'
+      successfully_exported: 'Exercise has been successfully exported.<br>ID: %{id}<br>Title: %{title}'
       export_failed: 'Export has failed.<br>ID: %{id}<br>Title: %{title}<br><br>Error: %{error}'
       error: 'An error occurred while contacting Codeharbor<br>Error: %{message}'
       checking_codeharbor: Checking if the exercise exists on Codeharbor.
diff --git a/spec/controllers/codeharbor_links_controller_spec.rb b/spec/controllers/codeharbor_links_controller_spec.rb
new file mode 100644
index 00000000..b057c32f
--- /dev/null
+++ b/spec/controllers/codeharbor_links_controller_spec.rb
@@ -0,0 +1,93 @@
+require 'rails_helper'
+
+describe CodeharborLinksController do
+  let(:user) { FactoryBot.create(:teacher) }
+  before(:each) { allow(controller).to receive(:current_user).and_return(user) }
+
+  describe 'GET #new' do
+    before { get :new }
+
+    expect_status(200)
+  end
+
+  describe 'GET #edit' do
+    let(:codeharbor_link) { FactoryBot.create(:codeharbor_link, user: user) }
+
+    before { get :edit, params: { id: codeharbor_link.id } }
+
+    expect_status(200)
+  end
+
+  describe 'POST #create' do
+    let(:post_request) { post :create, params: {codeharbor_link: params} }
+    let(:params) { {push_url: 'http://foo.bar/push', check_uuid_url: 'http://foo.bar/check', api_key: 'api_key'} }
+
+    it 'creates a codeharbor_link' do
+      expect { post_request }.to change(CodeharborLink, :count).by(1)
+    end
+
+    it 'redirects to user show' do
+      expect(post_request).to redirect_to(user)
+    end
+
+    context 'with invalid params' do
+      let(:params) { {push_url: '', check_uuid_url: '', api_key: ''} }
+
+      it 'does not create a codeharbor_link' do
+        expect { post_request }.not_to change(CodeharborLink, :count)
+      end
+
+      it 'redirects to user show' do
+        post_request
+        expect(response).to render_template(:new)
+      end
+    end
+  end
+
+  describe 'PUT #update' do
+    let(:codeharbor_link) { FactoryBot.create(:codeharbor_link, user: user) }
+    let(:put_request) { patch :update, params: {id: codeharbor_link.id, codeharbor_link: params} }
+    let(:params) { {push_url: 'http://foo.bar/push', check_uuid_url: 'http://foo.bar/check', api_key: 'api_key'} }
+
+    it 'updates push_url' do
+      expect { put_request }.to change { codeharbor_link.reload.push_url }.to('http://foo.bar/push')
+    end
+    it 'updates check_uuid_url' do
+      expect { put_request }.to change { codeharbor_link.reload.check_uuid_url }.to('http://foo.bar/check')
+    end
+    it 'updates api_key' do
+      expect { put_request }.to change { codeharbor_link.reload.api_key }.to('api_key')
+    end
+
+    it 'redirects to user show' do
+      expect(put_request).to redirect_to(user)
+    end
+
+    context 'with invalid params' do
+      let(:params) { {push_url: '', check_uuid_url: '', api_key: ''} }
+
+      it 'does not change codeharbor_link' do
+        expect { put_request }.not_to change { codeharbor_link.reload.attributes }
+      end
+
+      it 'redirects to user show' do
+        put_request
+        expect(response).to render_template(:edit)
+      end
+    end
+  end
+
+  describe 'DELETE #destroy' do
+    let!(:codeharbor_link) { FactoryBot.create(:codeharbor_link, user: user) }
+    let(:destroy_request) { delete :destroy, params: {id: codeharbor_link.id} }
+
+    it 'deletes codeharbor_link' do
+      expect { destroy_request }.to change(CodeharborLink, :count).by(-1)
+    end
+
+    it 'redirects to user show' do
+      expect(destroy_request).to redirect_to(user)
+    end
+  end
+end
+
diff --git a/spec/controllers/exercises_controller_spec.rb b/spec/controllers/exercises_controller_spec.rb
index 424a5290..3c5289c0 100644
--- a/spec/controllers/exercises_controller_spec.rb
+++ b/spec/controllers/exercises_controller_spec.rb
@@ -313,4 +313,203 @@ describe ExercisesController do
       expect_template(:edit)
     end
   end
+
+  RSpec::Matchers.define_negated_matcher :not_include, :include
+  # RSpec::Support::ObjectFormatter.default_instance.max_formatted_output_length = 99999
+
+  describe 'POST #export_external_check' do
+    render_views
+
+    let(:post_request) { post :export_external_check, params: { id: exercise.id } }
+    let!(:codeharbor_link) { FactoryBot.create(:codeharbor_link, user: user) }
+    let(:external_check_hash) { {message: message, exercise_found: true, update_right: update_right, error: error} }
+    let(:message) { 'message' }
+    let(:update_right) { true }
+    let(:error) {}
+
+    before { allow(ExerciseService::CheckExternal).to receive(:call).with(uuid: exercise.uuid, codeharbor_link: codeharbor_link).and_return(external_check_hash) }
+
+    it 'renders the correct contents as json' do
+      post_request
+      expect(JSON.parse(response.body).symbolize_keys[:message]).to eq('message')
+      expect(JSON.parse(response.body).symbolize_keys[:actions]).to(
+        include('button').and(include('Abort').and(include('Export')))
+      )
+      expect(JSON.parse(response.body).symbolize_keys[:actions]).to(
+        not_include('Retry').and(not_include('Hide'))
+      )
+    end
+
+    context 'when there is an error' do
+      let(:error) { 'error' }
+
+      it 'renders the correct contents as json' do
+        post_request
+        expect(JSON.parse(response.body).symbolize_keys[:message]).to eq('message')
+        expect(JSON.parse(response.body).symbolize_keys[:actions]).to(
+          include('button').and(include('Abort')).and(include('Retry'))
+        )
+        expect(JSON.parse(response.body).symbolize_keys[:actions]).to(
+          not_include('Create new').and(not_include('Export')).and(not_include('Hide'))
+        )
+      end
+    end
+
+    context 'when update_right is false' do
+      let(:update_right) { false }
+
+      it 'renders the correct contents as json' do
+        post_request
+        expect(JSON.parse(response.body).symbolize_keys[:message]).to eq('message')
+        expect(JSON.parse(response.body).symbolize_keys[:actions]).to(
+          include('button').and(include('Abort')).and(include('Create new'))
+        )
+        expect(JSON.parse(response.body).symbolize_keys[:actions]).to(
+          not_include('Retry').and(not_include('Export')).and(not_include('Hide'))
+        )
+      end
+    end
+  end
+
+  describe '#export_external_confirm' do
+    render_views
+
+    let!(:codeharbor_link) { FactoryBot.create(:codeharbor_link, user: user) }
+    let(:post_request) { post :export_external_confirm, params: {push_type: push_type, id: exercise.id, codeharbor_link: codeharbor_link.id} }
+    let(:push_type) { 'create_new' }
+    let(:error) {}
+    let(:zip) { 'zip' }
+
+    before do
+      allow(ProformaService::ExportTask).to receive(:call).with(exercise: exercise).and_return(zip)
+      allow(ExerciseService::PushExternal).to receive(:call).with(zip: zip, codeharbor_link: codeharbor_link).and_return(error)
+    end
+
+    it 'renders correct response' do
+      post_request
+
+      expect(response).to have_http_status(:success)
+      expect(JSON.parse(response.body).symbolize_keys[:message]).to(include('successfully exported'))
+      expect(JSON.parse(response.body).symbolize_keys[:status]).to(eql('success'))
+      expect(JSON.parse(response.body).symbolize_keys[:actions]).to(include('button').and(include('Close')))
+      expect(JSON.parse(response.body).symbolize_keys[:actions]).to(not_include('Retry').and(not_include('Abort')))
+    end
+
+    context 'when an error occurs' do
+      let(:error) { 'exampleerror' }
+
+      it 'renders correct response' do
+        post_request
+        expect(response).to have_http_status(:success)
+        expect(JSON.parse(response.body).symbolize_keys[:message]).to(include('failed').and(include('exampleerror')))
+        expect(JSON.parse(response.body).symbolize_keys[:status]).to(eql('fail'))
+        expect(JSON.parse(response.body).symbolize_keys[:actions]).to(include('button').and(include('Retry')).and(include('Close')))
+        expect(JSON.parse(response.body).symbolize_keys[:actions]).to(not_include('Abort'))
+      end
+    end
+
+    context 'without push_type' do
+      let(:push_type) {}
+
+      it 'responds with status 500' do
+        post_request
+        expect(response).to have_http_status(:internal_server_error)
+      end
+    end
+  end
+
+  describe '#import_uuid_check' do
+    let(:exercise) { FactoryBot.create(:dummy, uuid: SecureRandom.uuid) }
+    let!(:codeharbor_link) { FactoryBot.create(:codeharbor_link, user: user) }
+    let(:uuid) { exercise.reload.uuid }
+    let(:post_request) { post :import_uuid_check, params: {uuid: uuid} }
+    let(:headers) { {'Authorization' => "Bearer #{codeharbor_link.api_key}"} }
+
+    before { request.headers.merge! headers }
+
+    it 'renders correct response' do
+      post_request
+      expect(response).to have_http_status(:success)
+
+      expect(JSON.parse(response.body).symbolize_keys[:exercise_found]).to be true
+      expect(JSON.parse(response.body).symbolize_keys[:update_right]).to be true
+      expect(JSON.parse(response.body).symbolize_keys[:message]).to(include('has been found').and(include('Overwrite')))
+    end
+
+    context 'when api_key is incorrect' do
+      let(:headers) { {'Authorization' => 'Bearer XXXXXX'} }
+
+      it 'renders correct response' do
+        post_request
+        expect(response).to have_http_status(:unauthorized)
+      end
+    end
+
+    context 'when the user is cannot update the exercise' do
+      let(:codeharbor_link) { FactoryBot.create(:codeharbor_link, api_key: 'anotherkey') }
+
+      it 'renders correct response' do
+        post_request
+        expect(response).to have_http_status(:success)
+
+        expect(JSON.parse(response.body).symbolize_keys[:exercise_found]).to be true
+        expect(JSON.parse(response.body).symbolize_keys[:update_right]).to be false
+        expect(JSON.parse(response.body).symbolize_keys[:message]).to(include('has been found').and(not_include('Overwrite')))
+      end
+    end
+
+    context 'when the searched exercise does not exist' do
+      let(:uuid) { 'anotheruuid' }
+
+      it 'renders correct response' do
+        post_request
+        expect(response).to have_http_status(:success)
+
+        expect(JSON.parse(response.body).symbolize_keys[:exercise_found]).to be false
+        expect(JSON.parse(response.body).symbolize_keys[:message]).to(include('No corresponding exercise'))
+      end
+    end
+  end
+
+  describe 'POST #import_exercise' do
+    let(:codeharbor_link) { FactoryBot.create(:codeharbor_link, user: user) }
+    let(:imported_exercise) { exercise }
+    let(:post_request) { post :import_exercise, body: zip_file_content }
+    let(:zip_file_content) { 'zipped task xml' }
+    let(:headers) { {'Authorization' => "Bearer #{codeharbor_link.api_key}"} }
+
+    before do
+      request.headers.merge! headers
+      allow(ProformaService::Import).to receive(:call).and_return(imported_exercise)
+    end
+
+    it 'responds with correct status code' do
+      post_request
+      expect(response).to have_http_status(:created)
+    end
+
+    it 'calls service' do
+      post_request
+      expect(ProformaService::Import).to have_received(:call).with(zip: be_a(Tempfile).and(has_content(zip_file_content)), user: user)
+    end
+
+    context 'when import fails with ProformaError' do
+      before { allow(ProformaService::Import).to receive(:call).and_raise(Proforma::PreImportValidationError) }
+
+      it 'responds with correct status code' do
+        post_request
+        expect(response).to have_http_status(:bad_request)
+      end
+    end
+
+    context 'when import fails due to another error' do
+      before { allow(ProformaService::Import).to receive(:call).and_raise(StandardError) }
+
+      it 'responds with correct status code' do
+        post_request
+        expect(response).to have_http_status(:internal_server_error)
+      end
+    end
+  end
+
 end
diff --git a/spec/factories/codeharbor_link.rb b/spec/factories/codeharbor_link.rb
new file mode 100644
index 00000000..c960eb9a
--- /dev/null
+++ b/spec/factories/codeharbor_link.rb
@@ -0,0 +1,8 @@
+FactoryBot.define do
+  factory :codeharbor_link do
+    user { build(:teacher) }
+    push_url { 'http://push.url' }
+    check_uuid_url { 'http://check-uuid.url' }
+    sequence(:api_key) { |n| "api_key#{n}" }
+  end
+end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index f13a3edb..570c271b 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -20,6 +20,8 @@ unless RUBY_PLATFORM == 'java'
     SimpleCov.start('rails')
 end
 
+require 'webmock/rspec'
+
 RSpec.configure do |config|
   # These two settings work together to allow you to limit a spec run
   # to individual examples or groups you care about by tagging them with
diff --git a/spec/support/expectations/has_content.rb b/spec/support/expectations/has_content.rb
new file mode 100644
index 00000000..e0f5f60c
--- /dev/null
+++ b/spec/support/expectations/has_content.rb
@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+require 'rspec/expectations'
+
+RSpec::Matchers.define :has_content do |actual_content|
+  match do |file|
+    file.read == actual_content
+  end
+end