'Registering a new serializer populates the full registry. Refs #14823'

def test_register(self):

    serializers.register_serializer(u'json3', u'django.core.serializers.json')
    public_formats = serializers.get_public_serializer_formats()
    self.assertIn(u'json3', public_formats)
    self.assertIn(u'json2', public_formats)
    self.assertIn(u'xml', public_formats)
