CODEWITHSUNDEEP
python-3.xmockinggoogle-cloud-storagepytestpython-unittest.mock
AxA
AxA

Reputation: 349

Python unittest.mock google storage - how to achieve exceptions.NotFound as side effect

I've read a few tutorials on mocking in Python, but I'm still struggling :-/

For example, I have a function wrapping a call to google storage to write a blob.

I'd like to mock the google.storage.Client().bucket(bucket_name) method to return an exceptions.NotFound for a specific non-existent bucket. I'm using side_effect to set the excepted exception

Do you know what I'm doing wrong?

Below is what I tried (I'm using 2 files: main2.py and main2_test.py):

# main2.py
import logging
from google.cloud import storage

def _write_content(bucket_name, blob_name, content):
   storage_client = storage.Client()
   bucket = storage_client.bucket(bucket_name)
   blob = bucket.blob(blob_name)

   try:
        blob.upload_from_string(data=content)
        return True
    except Exception:
        logging.error("Failed to upload blob")
        raise

and

# main2_test.py
import pytest
from unittest.mock import patch
from google.api_core import exceptions
import main2


@patch("main2.storage.Client", autospec=True)
def test_write_content(clientMock):
    bucket_name = "not_existent_bucket"
    clientMock().bucket(bucket_name).side_effect = exceptions.NotFound

    with pytest.raises(exceptions.NotFound):
        main2._write_content(bucket_name, "a_blob_name", '{}')

Example call

pytest main2_test.py::test_write_content

Result

platform linux -- Python 3.7.7, pytest-5.4.3, py-1.9.0, pluggy-0.13.1
rootdir: /home/user/project, inifile: pytest.ini
plugins: requests-mock-1.8.0
collected 1 item                                                                                                                                                                                     

main2_test.py::test_write_content FAILED                                                                                                                                                       [100%]

============================================================================================== FAILURES ==============================================================================================
_________________________________________________________________________________________ test_write_content _________________________________________________________________________________________

clientMock = <MagicMock name='Client' spec='Client' id='139881522497360'>

    @patch("main2.storage.Client", autospec=True)
    def test_write_content(clientMock):
        bucket_name = "my_bucket"
        clientMock().bucket(bucket_name).side_effect = exceptions.NotFound
    
        with pytest.raises(exceptions.NotFound):
>           main2._write_content(bucket_name, "a_blob_name", '{}')
E           Failed: DID NOT RAISE <class 'google.api_core.exceptions.NotFound'>

main2_test.py:14: Failed
=====================================
FAILED main2_test.py::test_write_content - Failed: DID NOT RAISE <class 'google.api_core.exceptions.NotFound'>
=====================================

Upvotes: 3

Views: 4563

Answers (1)

MrBean Bremen
MrBean Bremen

Reputation: 16855

Your test has two problems: you are not mocking the method that shall actually raise (upload_from_string), and you are setting an exception class instead of an exception as side effect.

The following would work:

@patch("main2.storage.Client", autospec=True)
def test_write_content(clientMock):
    blob_mock = clientMock().bucket.return_value.blob.return_value  # split this up for readability
    blob_mock.upload_from_string.side_effect = exceptions.NotFound('testing')  # the exception is created here

    with pytest.raises(exceptions.NotFound):
        main2._write_content("not_existent", "a_blob_name", '{}')

Note also that setting a specific parameter for the bucket call has no effect, as it is called on a mock, and the argument is just ignored - I replaced it with return_value, which makes this clearer.

Upvotes: 3

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