LayoutTests/editing/inserting/redo.html

<script>
if (window.testRunner)
     testRunner.dumpEditingCallbacks();
</script>
<div id="test" contenteditable="true"></div>

<script>
window.getSelection().setPosition(document.getElementById("test"), 0);
document.execCommand("InsertText", false, "The caret should be at the end of this sentence.");
document.execCommand("Undo");
document.execCommand("Redo");
</script>