mozilla-release/testing/web-platform/tests/uievents/mouse/layout_change_should_fire_mouseover-manual.html

<!doctype html>
<html>
    <head>
        <title>Mouseover/enter is sent on layout change</title>
        <meta name="viewport" content="width=device-width">
        <script src="/resources/testharness.js"></script>
        <script src="/resources/testharnessreport.js"></script>
        <style>
            #spacer {
                height: 100px;
                width: 100px;
            }
            #red {
                background-color: rgb(255, 0, 0);
                position: absolute;
                z-index: 0;
                left: 0px;
                top: 0px;
                height: 100px;
                width: 100px;
            }
            #blue {
                background-color: rgb(0, 0, 255);
                position: absolute;
                z-index: 1;
                left: 0px;
                top: 0px;
                height: 100px;
                width: 100px;
            }
            #blue:hover {
                background-color: rgb(255, 255, 0);
            }
        </style>
    </head>
    <body onload="run();">
        <div id="spacer"></div>
        <div id="red"></div>
        <h4>Test Description: Tests that the mouseover event is fired and the element has a hover effect when the element underneath the mouse cursor is changed.
            <ol>
                <li>Put your mouse over the red rectangle</li>
                <li>Click the primary mouse button</li>
            </ol>
        </h4>
        <script type="text/javascript">
            var testMouseOver = async_test('Tests that the mouseover event is fired and the element has a hover effect when the element underneath the mouse cursor is changed.');

            var eventList = [];
            function addBlue() {
                document.body.innerHTML += '<div id="blue"></div>';
                var blue = document.getElementById("blue");
                var events = ['mouseover', 'mousemove', 'mouseout', 'mouseenter', 'mouseleave'];
                events.forEach(function (event) {
                    blue.addEventListener(event, checkHoverEffect);
                });
                testMouseOver.step_timeout(function () {
                   checkEventSequence();
                }, 2500);
            }

            function checkEventSequence() {
                var result = eventList.join();
                assert_true(result == 'mouseover,mouseenter');
                testMouseOver.done();
            }

            function run() {
                document.addEventListener('click', addBlue);
            }

            function checkHoverEffect(event) {
                eventList.push(event.type);
                testMouseOver.step(function () {
                  assert_equals(event.target.id, "blue");
                  assert_equals(getComputedStyle(event.target).backgroundColor, "rgb(255, 255, 0)");
                  if (event.type == "mouseenter") {
                      checkEventSequence();
                  }
              });
            }
        </script>
    </body>
</html>