This tests pasting text ('foo\nbar') into a list item. The last bit of content in the incoming fragment should be merged with the paragraph after the position being pasted into.

Before insertion:
| <ul>
|   <li>
|     <div>
|       "Item 1"

After insertion:
| <ul>
|   <li>
|     <div>
|       "Item foo"
|     <div>
|       "bar<#selection-caret>1"