This test splits a text node by inserting a new paragraph and bolds the the first half.
If splitTextNode correctly reapplied the split, undo and redo should preserve the style. (See bug 42941).

before undo:
| <b>
|   "<#selection-anchor>he<#selection-focus>"
| <div>
|   "llo"

after undo:
| "he<#selection-caret>llo"

after redo:
| <b>
|   "<#selection-anchor>he<#selection-focus>"
| <div>
|   "llo"