Note that the `create` action doesn't create an image but updates an
answer instead. We're removing the references to `:create` in the
abilities since it isn't used.
In the future we might change the form to add an image to an answer
because it's been broken for ages since it shows all the attached
images.
Adding, modifiying, and/or deleting questions for an already started
poll is far away from being democratic and can lead to unwanted side
effects like missing votes in the results or stats.
So, from now on, only modifiying questions will be possible only if
the poll has not started yet.
System tests are used to test the application from the user's point of
view. To test for specific exceptions, particularly regarding
authorization permissions, controller tests fit better.
Another option would be to test the page displayed shows a certain text,
like "Internal server error". I'm choosing controller tests because
they're faster and we're basically testing the same scenario many times
and we've already got a test checking what happens when users access a
page raising an exception.
