anchor.diff:  image:.pics/ui_content_testing.png[Native UI component: Calculator  gedit]
   
   The implementation of the test case is very simple, you can just mix web and native testing methods. Take a look at the file: link:part_01/example_xfce/case1/sakuli_demo.js[`part_01/example_xfce/case1/sakuli_demo.js`].
  -[source, js]
  +[source,js]
   ----
   _dynamicInclude($includeFolder);
   var testCase = new TestCase(40, 60);
  
positive.code: To get a feeling how Sakuli reacts on errors we will modify the testcase definition `sakuli_demo.js` to a not present link validation and force an error through this:
  
  .link:part_02/sakuli-tests/example_xfce/case1/sakuli_demo.js[`part_02/sakuli-tests/example_xfce/case1/sakuli_demo.js`]
  [soruce,js]
  ----
  ...
  try {
  
negative.code: 
  Now we can configure the runtime environment there we use the Docker image `consol/sakuli-ubuntu-xfce` and for the second environment `consol/sakuli-centos-xfce` container where we mount in our test case definition. To make it easy to start the container, we used https://docs.docker.com/compose/[Docker Compose] to define the setup in the file link:part_01/docker-compose.yml[`part_01/docker-compose.yml`]:
  
  [source,yaml]
  ----
  sakuli_test_ubuntu_firefox:
    image: consol/sakuli-ubuntu-xfce:dev
  