django unittest without database connection

Question

I'm trying to write a unittest that will check if the correct error message is returned in case the database connection hits exception. I've tried to use connection.creation.destroy_test_db(':memory:') but it didn't work as I expected. I suppose I should either remove the tables or somehow cut the db connection. Is any of those possible?

Answer 1

I found my answer in the presentation Testing and Django by Carl Meyer. Here is how I did it:

from django.db import DatabaseError
from django.test import TestCase
from django.test.client import Client
import mock

class NoDBTest(TestCase):
    cursor_wrapper = mock.Mock()
    cursor_wrapper.side_effect = DatabaseError

    @mock.patch("django.db.backends.util.CursorWrapper", cursor_wrapper)
    def test_no_database_connection(self):
        response = self.client.post('/signup/', form_data)
        self.assertEqual(message, 'An error occured with the DB')

Answer 2

I was looking for django's actual http response code in case of a database connection timeout when using pymysql. The following test confirmed it's a 401 Unauthorized when pymysql raises an OperationalError.

from unittest.mock import patch

import pymysql
from django.test import TestCase, Client


class TestDatabaseOutage(TestCase):
    client = None

    def setUp(self):
        self.client = Client()

    def test_database_connection_timeout_returns_401(self):
        with patch.object(pymysql, 'connect') as connect_method:
            message = "Can't connect to MySQL server on 'some_database.example.com' ([Errno 110] Connection timed out)"
            connect_method.side_effect = pymysql.OperationalError(2003, message)
            response = self.client.get('/')
            self.assertEqual(response.status_code, 401)

Answer 3

Sounds like this is a job for mocking. For example, if you are using MySQL, you can put a side_effect on connect method, like this:

from django.test import TestCase
from mock import patch
import MySQLdb


class DBTestCase(TestCase):
    def test_connection_error(self):
        with patch.object(MySQLdb, 'connect') as connect_method:
            connect_method.side_effect = Exception("Database Connection Error")

            # your assertions here

Hope that helps.