how do I test methods using boto3 with moto

I am writing test cases for a quick class to find / fetch keys from s3, using boto3. I have used moto in the past to test boto (not 3) code but am trying to move to boto3 with this project, and running into an issue:

class TestS3Actor(unittest.TestCase):
    @mock_s3
    def setUp(self):
        self.bucket_name = 'test_bucket_01'
        self.key_name = 'stats_com/fake_fake/test.json'
        self.key_contents = 'This is test data.'
        s3 = boto3.session.Session().resource('s3')
        s3.create_bucket(Bucket=self.bucket_name)
        s3.Object(self.bucket_name, self.key_name).put(Body=self.key_contents)

error:

...
File "/Library/Python/2.7/site-packages/botocore/vendored/requests/packages/urllib3/connectionpool.py", line 344, in _make_request
self._raise_timeout(err=e, url=url, timeout_value=conn.timeout)
File "/Library/Python/2.7/site-packages/botocore/vendored/requests/packages/urllib3/connectionpool.py", line 314, in _raise_timeout
if 'timed out' in str(err) or 'did not complete (read)' in str(err):  # Python 2.6
TypeError: __str__ returned non-string (type WantWriteError)
botocore.hooks: DEBUG: Event needs-retry.s3.CreateBucket: calling handler <botocore.retryhandler.RetryHandler object at 0x10ce75310>

It looks like moto is not mocking out the boto3 call correctly - how do I make that work?