Disable DB Access for Speedy Unit Tests
Disable Django DB Access for Speedy Unit Tests
A recurring problem in my career over the past few years has been introducing testing into legacy django apps which tend to suffer the problems of a typical “monolythic app”.
Django comes with great built-in support for integration-style tests, with in-memory databases standing in for actual databases, all of your migrations running anew per test, and so on.
I have yet to meet a django app with well-enough maintained migrations for this to be possible; first because maintaining historical rebuilding of your external resources tends to be a low priority in environments which embrace the framework for its enabling of fast-moving iterations, as it probably should be, and second because it makes running the tests so slow as to discourage developers from actually running them.
Recently finding myself in such an environment again, I had created certain pieces of code I would like to unit test (not integration, simply test certain heavily shared individual functions to ensure that their behavior not inadvertently change when working on the specific requirements of one of the users of said functions).
Inspired by a few blog posts about speeding up tests in django, in part by disabling db access and a few about mock strategies I created the following base class for my unit tests:
import mock
import unittest
import gas
from django.db.backends.utils import CursorWrapper
disabled_cursor = mock.Mock()
disabled_cursor.side_effect = RuntimeError("db access disabled")
disabled_cursor.WRAP_ERROR_ATTRS = CursorWrapper.WRAP_ERROR_ATTRS
# raise error if test code attempts to access db
@mock.patch("django.db.backends.utils.CursorWrapper", disabled_cursor)
@mock.patch("django.db.backends.utils.CursorDebugWrapper", disabled_cursor)
class BaseGasVolumesTestCase(unittest.TestCase):
# this method intentionally not mock.patch()ed to prevent db access,
# it will run for all subclasses, ensuring none can access the db
def test_db_access_raises_error(self):
from gas.queries import get_clients
with self.assertRaises(RuntimeError) as ctxt:
cus = get_clientutilities()
self.assertEqual(ctxt.exception.message, "db access disabled")Each of your tests then must mock out each of the methods it invokes which would otherwise touch the database:
# raise error if test code attempts to access db
@mock.patch("django.db.backends.utils.CursorWrapper", disabled_cursor)
@mock.patch("django.db.backends.utils.CursorDebugWrapper", disabled_cursor)
class TestGasVolumesForecastedDemand(BaseGasVolumesTestCase):
@mock.patch('gas.volumes.forecasteddemand.DailyForecastedDemand.save', side_effect=None)
@mock.patch('gas.volumes.forecasteddemand.MonthlyForecastedDemand.save', side_effect=None)
def test_save_forecasteddemand(self, monthly_save, daily_save):
# behavior when insert is performed on db
with mock.patch('gas.volumes.forecasteddemand.DailyForecastedDemand.objects.get_or_create',
side_effect=get_or_create_isnew_true):
(fd, isnew) = save_forecasteddemand('daily', '2016-10-31', 48, 87, 10, 'Utility Group', 99)
self.assertTrue(isinstance(fd, DailyForecastedDemand))
self.assertTrue(isnew)
with mock.patch('gas.volumes.forecasteddemand.MonthlyForecastedDemand.objects.get_or_create',
side_effect=get_or_create_isnew_true):
(fd, isnew) = save_forecasteddemand('monthly', '2016-10-01', 48, 87, 310, 'Utility Group')
self.assertTrue(isinstance(fd, MonthlyForecastedDemand))
self.assertTrue(isnew)
with self.assertRaises(AttributeError):
max_dths = fd.max_dths
# behavior when record exists and values haven't changed
with mock.patch('gas.volumes.forecasteddemand.DailyForecastedDemand.objects.get_or_create',
side_effect=get_or_create_isnew_false):
(fd, isnew) = save_forecasteddemand('daily', '2016-10-31', 48, 87, 10, 'Utility Group', 99)
self.assertTrue(isinstance(fd, DailyForecastedDemand))
self.assertFalse(isnew)
with mock.patch('gas.volumes.forecasteddemand.MonthlyForecastedDemand.objects.get_or_create',
side_effect=get_or_create_isnew_false):
(fd, isnew) = save_forecasteddemand('monthly', '2016-10-01', 48, 87, 310, 'Utility Group')
self.assertTrue(isinstance(fd, MonthlyForecastedDemand))
self.assertFalse(isnew)
with self.assertRaises(AttributeError):
max_dths = fd.max_dths
# behavior when record exists and non-key values have changed
with mock.patch('gas.volumes.forecasteddemand.DailyForecastedDemand.objects.get_or_create',
side_effect=get_or_create_raises_integrity_error):
with mock.patch('gas.volumes.forecasteddemand.DailyForecastedDemand.objects.get',
side_effect=get):
(fd, isnew) = save_forecasteddemand('daily', '2016-10-31', 48, 87, 10, 'Utility Group', 99)
self.assertTrue(isinstance(fd, DailyForecastedDemand))
self.assertFalse(isnew)
with mock.patch('gas.volumes.forecasteddemand.MonthlyForecastedDemand.objects.get_or_create',
side_effect=get_or_create_raises_integrity_error):
with mock.patch('gas.volumes.forecasteddemand.MonthlyForecastedDemand.objects.get',
side_effect=get):
(fd, isnew) = save_forecasteddemand('monthly', '2016-10-01', 48, 87, 310, 'Utility Group')
self.assertTrue(isinstance(fd, MonthlyForecastedDemand))
self.assertFalse(isnew)
with self.assertRaises(AttributeError):
max_dths = fd.max_dths
@mock.patch("gas.volumes.forecasteddemand.get_utility_by_id", return_value=CONED)
@mock.patch("gas.volumes.forecasteddemand.get_client_by_id", return_value=None)
def test_fetch_demand_for_client_raises_bad_creds(self, client_by_id, utility_by_id):
gas.volumes.forecasteddemand.get_logincredentials._creds = MOCK_LOGINCREDENTIALS
with self.assertRaises(ValueError) as ctxt:
fds = fetch_demand_for_client('2016-08-01', 14, -1, dummy_generator)
self.assertEqual(ctxt.exception.message[:27], 'No login creds for (-1, 14)')
@mock.patch('gas.volumes.forecasteddemand.DailyForecastedDemand.save', side_effect=None)
@mock.patch('gas.volumes.forecasteddemand.MonthlyForecastedDemand.save', side_effect=None)
@mock.patch('gas.volumes.forecasteddemand.DailyForecastedDemand.objects.get_or_create', side_effect=get_or_create_isnew_true)
@mock.patch("gas.volumes.forecasteddemand.get_utility_by_id", return_value=CONED)
@mock.patch("gas.volumes.forecasteddemand.get_client_by_id", return_value=ALPHA)
@mock.patch("gas.volumes.forecasteddemand.get_logincredentials", return_value=ALPHACONED_LOGINCREDENTIALS)
def test_fetch_demand_for_client(self, creds, client_by_id, utility_by_id,
save_func, monthly_save, daily_save):
with mock.patch('gas.volumes.forecasteddemand.MonthlyForecastedDemand.objects.get_or_create',
side_effect=get_or_create_isnew_true):
fds = fetch_demand_for_client('2016-10-01',
CONED['utility_id'],
ALPHA['client_id'],
alpha_coned_usage_generator)
# (31 daily * 3 ugs) + (1 month * 3 ugs) = 96
self.assertEqual(96, len(fds))
for fd in fds:
if isinstance(fd, DailyForecastedDemand):
if fd.utility_group == 'UG One':
self.assertEqual(2.0, fd.decatherms)
elif fd.utility_group == 'UG Tw0':
self.assertEqual(3.0, fd.decatherms)
elif fd.utility_group == '':
self.assertEqual(5.0, fd.decatherms)
elif isinstance(fd, MonthlyForecastedDemand):
if fd.utility_group == 'UG One':
self.assertEqual(2.0 * 31, fd.decatherms)
elif fd.utility_group == 'UG Tw0':
self.assertEqual(3.0 * 31, fd.decatherms)
elif fd.utility_group == '':
self.assertEqual(5.0 * 31, fd.decatherms)