chromium/third_party/blink/web_tests/external/wpt/editing/other/link-boundaries-insertion.html

<!DOCTYPE HTML>
<meta charset=utf-8>
<title>Placing selection and typing inside empty elements</title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="../include/editor-test-utils.js"></script>

<div contenteditable></div>

<script>
  const utils = new EditorTestUtils( document.querySelector( 'div[contenteditable]' ) );

  test( () => {
    utils.setupEditingHost( `<p><a href="https://example.com" id="test-end">Link</a></p>` );

    const target = document.querySelector( '#test-end' );
    const range = document.createRange();
    const selection = getSelection();

    range.selectNodeContents( target );
    selection.removeAllRanges();
    selection.addRange( range );
    selection.collapseToEnd();

    document.execCommand( 'insertText', false, 'a' );
    assert_equals( target.innerHTML, 'Linka', 'The text should be inserted into the link' );
  }, 'Insert text into the selection at the end of a link' );

  test( () => {
    utils.setupEditingHost( `<p><a href="https://example.com" id="test-beginning">Link</a></p>` );

    const target = document.querySelector( '#test-beginning' );
    const range = document.createRange();
    const selection = getSelection();

    range.selectNodeContents( target );
    selection.removeAllRanges();
    selection.addRange( range );
    selection.collapseToStart();

    document.execCommand( 'insertText', false, 'a' );
    assert_equals( target.innerHTML, 'aLink', 'The text should be inserted into the link' );
  }, 'Insert text into the selection at the beginning of a link' );
</script>