chromium/src/third_party/blink/web_tests/editing/pasteboard/5665299.html

<div id="description">This tests for a bug where pasting plain text into an empty contenteditable div would create paragraphs held in clones of the contenteditable div.  To run it manually, do a Paste and Match style and then inspect the editable region.  It should contain paragraphs held in regular divs.</div>
<textarea id="copy">test


</textarea>
<div id="paste" contenteditable="true"><br></div>

<script>
if (window.testRunner)
    testRunner.dumpAsText();
    
copy = document.getElementById("copy");
copy.focus();
document.execCommand("SelectAll");
document.execCommand("Copy");

paste = document.getElementById("paste");
paste.focus();
document.execCommand("PasteAndMatchStyle");
document.body.innerText = document.getElementById("description").innerText + "\n\n" + paste.innerHTML;
</script>