This tests ensures formatBlock removes a pre when formatting multiple paragraphs inside the pre.

Formatting all paragraphs by h3 yields:
| "\n"
| <h3>
|   "<#selection-anchor>hello"
|   <br>
|   "\n"
|   "world"
|   <br>
|   "\n"
|   "webkit<#selection-focus>"
| "\n"

Undo yields:
| "\n"
| <pre>
|   "<#selection-anchor>hello\n\nworld\n\nwebkit<#selection-focus>\n"
| "\n"

Formatting all but the last paragraph by h3 yields:
| "\n"
| <pre>
|   <h3>
|     "<#selection-anchor>hello"
|     "\n"
|     "world"
|     "\n"
|   "<#selection-focus>webkit\n"
| "\n"

Undo yields:
| "\n"
| <pre>
|   "<#selection-anchor>hello\n\nworld\n\n<#selection-focus>webkit\n"
| "\n"

Formatting all but the first paragraph by h3 yields:
| "\n"
| <pre>
|   "hello\n"
|   <h3>
|     "<#selection-anchor>\n"
|     "world"
|     "\n"
|     "webkit<#selection-focus>"
| "\n"