The idea behind the test was something simple to demonstrate that PHP does, indeed, throw a fit about trying to send headers after they've already been "sent".  I agree that it's highly unlikely that this use would be seen in practice, especially by someone who knows what they're doing.  However, more complex applications which follow the guidelines appropriately might still encounter this issue if, say, some part of CI itself calls ```set_status_header()``` after the first line of output has already been sent.  This error message clutters the output, making it harder to identify the actual issue.

As to why I chose 2.1.3...  Probably mostly that I knew my local copy of *that* was clean.