boto3_mock.py

import botocore
from botocore.exceptions import ClientError
from mock import patch
import boto3
from util import get_credentials 

orig = botocore.client.BaseClient._make_api_call

def mock_get_cluster_credentials(self, operation_name, kwarg):
    if operation_name == 'GetClusterCredentials':
        return {"DbUser": "abc", "DbPassword":"abc"}
    return orig(self, operation_name, kwarg)

def get_redshift()
with patch('botocore.client.BaseClient._make_api_call', new=mock_make_api_call):
    # Should return actual result
    o = get_credentials(mocked_rs_client,'host','port')
    # Should return mocked exception
    assert 'DbUser' in o
    assert 'DbPassword' in o