def test_list_buckets(self):
"""This is replacing a private member with a mock"""
# setup
foobar = Foobar()
s3_mock = MagicMock()
s3_mock.list_buckets.return_value = {'bucketa', 'bucketb'}
foobar.s3 = s3_mock
# exercise
result = foobar._list_buckets()
# verify
self.assertIn('bucketa', result)
