LayoutTests/editing/inserting/multiple-lines-selected.html

<script>
if (window.layoutTestController)
     layoutTestController.dumpEditingCallbacks();
</script>
<p>This tests inserting a paragraph separator into a selection that spans multiple paragraphs.  'ar' should be on the line after 'f' and the caret should be just before the 'a'.</p>
<div id="test" contenteditable="true"><div>foo</div><div>bar</div></div>

<script>
var s = window.getSelection();
var e = document.getElementById("test");

s.setPosition(e, 0);
s.modify("move", "forward", "character");
s.modify("extend", "forward", "line");

document.execCommand("InsertParagraph");

</script>