thoughtbot/shoulda-matchers — pull request #511 by jacobsimeon (2014-04-26 05:33:28+00:00)
Title: Check correct columns are present in join table

The `have_and_belong_to_many` matcher could give a false positive if the
join table is present but does not contain the correct columns. Check to
see if the columns exist in the join table and provide a meaningful
failure message if one or more of the columns are not present.