'This is invoked by test_main to ensure that it runs after
calling generate.main().
There should be exactly three merge comment headers
in our merged .po file. This counts them to be sure.
A merge comment looks like this:
# #-#-#-#-#  django-partial.po (0.1a)  #-#-#-#-#'

def assert_merge_headers(self, locale):

    path = os.path.join(self.configuration.get_messages_dir(locale), 'django.po')
    pof = pofile(path)
    pattern = re.compile('^#-#-#-#-#', re.M)
    match = pattern.findall(pof.header)
    self.assertEqual(len(match), 3, msg=('Found    %s    (should    be    3)    merge    comments    in    the    header    for    %s' % (len(match), path)))
