chromium/third_party/blink/web_tests/editing/deleting/merge-different-styles.html

<!doctype html>
<script src="../../resources/testharness.js"></script>
<script src="../../resources/testharnessreport.js"></script>
<script src="../assert_selection.js"></script>
<script>
// This places the caret before the 'b' in 'bar' and Deletes. 'foo' and 'bar'
// should end up on the same line, but neither should change style.
selection_test(
    [
        '<div contenteditable>',
            '<div>foo</div>',
            '<div style="font-weight: bold;">|bar</div>',
        '</div>',
    ],
    'Delete',
    [
        '<div contenteditable>',
            '<div>foo|<span style="font-weight: bold;">bar</span></div>',
        '</div>',
    ]);
</script>