This tests that the methods of the EventTarget interface work
correctly.
There are six sub-tests (a rectangle for each). These are:
- Sub-test 1: test adding a listener with addEventListener.
- Sub-test 2: test adding a listener with addEventListener then
removing it with removeEventListener.
- Sub-test 3: test adding a listener for an event type with incorrect casing.
- Sub-test 4: test adding a listener with addEventListenerNS.
- Sub-test 5: test adding a listener with addEventListenerNS then
removing it with removeEventListener.
- Sub-test 6: test adding a listener with addEventListener then
removing it with removeEventListenerNS.
The test has been passed if all six rectangles are blue.