This is a layout test for rdar://problem/4370209 "Reproducible crash when pasting over whitespace:pre text". The text below is selected, copied, and pasted over itself. You'll see foo/nbar if successful.
foo
bar
execCopyCommand: <div id="test" class="editing"> <pre>foo bar</pre> </div>
execPasteCommand: <div id="test" class="editing"> <pre>foo bar</pre> </div>