How to mock a custom exception in python3? - unit-testing

Question

I'm doing some unit test works in python using unittest module. When i try to unittest for the custom exception, it seems like it's not working. Below is my code
# src.py
from exceptions import ClusterException, IndexingException
from utils import create_index, index_to_es
def method(bucket, key, file):
try:
s3_obj = get_object(bucket, key)
....
....
create_index(index_name, index_mapping)
index_to_es(df)
except ClusterException as e:
raise ClusterException(e)
except Exception:
raise IndexingException(e)
Here i need to test for the ClusterException exception block. So i'm mocking create_index() method to raise a ClusterException error. My testing code is
# test_src.py
with mock.patch('src.ClusterException') as mocked_cluster_exception:
mocked_cluster_exception.side_effect = ClusterException("Bad Cluster Error")
with mock.patch('src.create_index') as mocked_create_index:
mocked_create_index.side_effect = ClusterException("Index creation error")
self.assertRaises(ClusterException, method, 'bucket', 'key', 'file')
And my exception file is
# exceptions.py
class ClusterException(Exception):
pass
class IndexingException(Exception):
pass
But when i run this the testing is getting failed with below message. What am i missing here?
TypeError: catching classes that do not inherit from BaseException is not allowed

Answer 1

You don't need to patch the src.ClusterException. You should patch the create_index() function to raise a ClusterException.
E.g.
src.py:
from exceptions import ClusterException, IndexingException
from utils import create_index
def method(bucket, key, file):
try:
index_name = 'index_name'
index_mapping = 'index_mapping'
create_index(index_name, index_mapping)
except ClusterException as e:
print(e)
raise ClusterException(e)
except Exception as e:
raise IndexingException(e)
utils.py:
def create_index(name, map):
pass
exceptions.py:
class ClusterException(Exception):
pass
class IndexingException(Exception):
pass
test_src.py:
from unittest import mock, main, TestCase
from exceptions import ClusterException
from src import method
class TestSrc(TestCase):
def test_method_to_raise_cluster_exception(self):
with mock.patch('src.create_index') as mocked_create_index:
mocked_create_index.side_effect = ClusterException("Index creation error")
self.assertRaises(ClusterException, method, 'bucket', 'key', 'file')
mocked_create_index.assert_called_once_with('index_name', 'index_mapping')
if __name__ == '__main__':
main()
unit test result:
Index creation error
.
----------------------------------------------------------------------
Ran 1 test in 0.001s
OK
Name Stmts Miss Cover Missing
------------------------------------------------------------------------
src/stackoverflow/68203609/exceptions.py 4 0 100%
src/stackoverflow/68203609/src.py 12 2 83% 13-14
src/stackoverflow/68203609/test_src.py 11 0 100%
src/stackoverflow/68203609/utils.py 2 1 50% 2
------------------------------------------------------------------------
TOTAL 29 3 90%