[Python] Exception handling in FastAPI

Seeing issue in unit test of exception case in FastAPI route.

Having following route configuration:

@router.get("/{user_id}", response_model=UserDbData, responses={
404: {"model": ErrorMessage},
500: {"model": ErrorMessage}
})
def get_user(user_id: str, db_session: Session = db_session):
"""Route for providing user information
"""
log.info(f"Handling user get request for id: {user_id}")

user: UserDbData
try:
user: UserDbData = UserService(db_session).get_user(user_id)
except UserInvalidException:
log.error(f"User_id:{user_id} do not exist.")
return error_response(
status_code=status.HTTP_404_NOT_FOUND,
message=ErrorMessage(detail=f"User_id:{user_id} do not exist.")
)
except UserReadException:
log.error(f"Issue in querying data for user_id:{user_id}")
return error_response(
status_code=status.HTTP_500_INTERNAL_SERVER_ERROR,
message=ErrorMessage(detail=f"Issue in querying data for user_id:{user_id}")
)
else:
log.debug(f"User info for id: {user_id}, is: {user}")
return user


When I am trying to test the exception cases of the route, I am not able to get response from except clause:

@patch('user.service.UserService.get_user')
def test_user_get_invalid_user_response(mock_get_user):
"""Testing get user route - invalid user respose case"""
mock_get_user.side_effect = UserInvalidException("")
response = client.get("/user/sam21")
assert response.status_code == 404


I am getting following issue in pytest:

self = <MagicMock name='get_user' id='4359134512'>, args = ('sam21',), kwargs = {}, effect = UserInvalidException('')

def _execute_mock_call(self, /, *args, **kwargs):
# separate from _increment_mock_call so that awaited functions are
# executed separately from their call, also AsyncMock overrides this method

effect = self.side_effect
if effect is not None:
if _is_exception(effect):
> raise effect E health_manager.user.exceptions.UserInvalidException

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