[Django]-Django unit tests without a db

Generally tests in an application can be classified in to two categories

1. Unit tests, these test the individual snippets of code in insolation and do not require to go to the database
2. Integration test cases which actually go to the database and test the fully integrated logic.

Django supports both unit and integration tests.

Unit tests, do not require to setup and tear down database and these we should inherit from SimpleTestCase.

from django.test import SimpleTestCase


class ExampleUnitTest(SimpleTestCase):
    def test_something_works(self):
        self.assertTrue(True)

For integration test cases inherit from TestCase in turn inherits from TransactionTestCase and it will setup and tear down the database before running each test.

from django.test import TestCase


class ExampleIntegrationTest(TestCase):
    def test_something_works(self):
        #do something with database
        self.assertTrue(True)

This strategy will ensure that database in created and destroyed only for the test cases that access the database and therefore tests will be more efficient

From django.test.simple

  warnings.warn(
      "The django.test.simple module and DjangoTestSuiteRunner are deprecated; "
      "use django.test.runner.DiscoverRunner instead.",
      RemovedInDjango18Warning)

So override DiscoverRunner instead of DjangoTestSuiteRunner.

 from django.test.runner import DiscoverRunner
 
 class NoDbTestRunner(DiscoverRunner):
   """ A test runner to test without database creation/deletion """
 
   def setup_databases(self, **kwargs):
     pass
      
   def teardown_databases(self, old_config, **kwargs):
     pass

Use like that :

python manage.py test --testrunner=app.filename.NoDbTestRunner app

I chose to inherit from django.test.runner.DiscoverRunner and make a couple of additions to the run_tests method.

My first addition checks to see if setting up a db is necessary and allows the normal setup_databases functionality to kick in if a db is necessary. My second addition allows the normal teardown_databases to run if the setup_databases method was allowed to run.

My code assumes that any TestCase that inherits from django.test.TransactionTestCase (and thus django.test.TestCase) requires a database to be setup. I made this assumption because the Django docs say:

If you need any of the other more complex and heavyweight Django-specific features like … Testing or using the ORM … then you should use TransactionTestCase or TestCase instead.

https://docs.djangoproject.com/en/1.6/topics/testing/tools/#django.test.SimpleTestCase

mysite/scripts/settings.py

from django.test import TransactionTestCase     
from django.test.runner import DiscoverRunner


class MyDiscoverRunner(DiscoverRunner):
    def run_tests(self, test_labels, extra_tests=None, **kwargs):
        """
        Run the unit tests for all the test labels in the provided list.

        Test labels should be dotted Python paths to test modules, test
        classes, or test methods.

        A list of 'extra' tests may also be provided; these tests
        will be added to the test suite.

        If any of the tests in the test suite inherit from
        ``django.test.TransactionTestCase``, databases will be setup. 
        Otherwise, databases will not be set up.

        Returns the number of tests that failed.
        """
        self.setup_test_environment()
        suite = self.build_suite(test_labels, extra_tests)
        # ----------------- First Addition --------------
        need_databases = any(isinstance(test_case, TransactionTestCase) 
                             for test_case in suite)
        old_config = None
        if need_databases:
        # --------------- End First Addition ------------
            old_config = self.setup_databases()
        result = self.run_suite(suite)
        # ----------------- Second Addition -------------
        if need_databases:
        # --------------- End Second Addition -----------
            self.teardown_databases(old_config)
        self.teardown_test_environment()
        return self.suite_result(suite, result)

Finally, I added the following line to my project’s settings.py file.

mysite/settings.py

TEST_RUNNER = 'mysite.scripts.settings.MyDiscoverRunner'

Now, when running only non-db-dependent tests, my test suite runs an order of magnitude faster! 🙂

Updated: also see this answer for using a third-party tool pytest.

@Cesar is right. After accidentally running ./manage.py test --settings=no_db_settings, without specifying an app name, my development database was wiped out.

For a safer manner, use the same NoDbTestRunner, but in conjunction with the following mysite/no_db_settings.py:

from mysite.settings import *

# Test runner with no database creation
TEST_RUNNER = 'mysite.scripts.testrunner.NoDbTestRunner'

# Use an alternative database as a safeguard against accidents
DATABASES['default']['NAME'] = '_test_mysite_db'

You need to create a database called _test_mysite_db using an external database tool. Then run the following command to create the corresponding tables:

./manage.py syncdb --settings=mysite.no_db_settings

If you’re using South, also run the following command:

./manage.py migrate --settings=mysite.no_db_settings

OK!

You can now run unit tests blazingly fast (and safe) by:

./manage.py test myapp --settings=mysite.no_db_settings

As an alternative to modifying your settings to make NoDbTestRunner “safe”, here’s a modified version of NoDbTestRunner that closes the current database connection and removes the connection information from settings and the connection object. Works for me, test it in your environment before relying on it 🙂

class NoDbTestRunner(DjangoTestSuiteRunner):
    """ A test runner to test without database creation """

    def __init__(self, *args, **kwargs):
        # hide/disconnect databases to prevent tests that 
        # *do* require a database which accidentally get 
        # run from altering your data
        from django.db import connections
        from django.conf import settings
        connections.databases = settings.DATABASES = {}
        connections._connections['default'].close()
        del connections._connections['default']
        super(NoDbTestRunner,self).__init__(*args,**kwargs)

    def setup_databases(self, **kwargs):
        """ Override the database creation defined in parent class """
        pass

    def teardown_databases(self, old_config, **kwargs):
        """ Override the database teardown defined in parent class """
        pass

Another solution would be to have your test class simply inherit from unittest.TestCase instead of any of Django’s test classes. The Django docs (https://docs.djangoproject.com/en/2.0/topics/testing/overview/#writing-tests) contain the following warning about this:

Using unittest.TestCase avoids the cost of running each test in a transaction and flushing the database, but if your tests interact with the database their behavior will vary based on the order that the test runner executes them. This can lead to unit tests that pass when run in isolation but fail when run in a suite.

However, if your test doesn’t use the database, this warning needn’t concern you and you can reap the benefits of not having to run each test case in a transaction.

The above solutions are fine too. But the following solution will also reduce the db creation time if there are more number of migrations.
During unit testing, running syncdb instead of running all the south migrations will be much faster.

SOUTH_TESTS_MIGRATE = False # To disable migrations and use syncdb
instead

My web host only allows creating and dropping databases from their Web GUI, so I was getting a “Got an error creating the test database: Permission denied” error when trying to run python manage.py test.

I’d hoped to use the –keepdb option to django-admin.py but it doesn’t seem to be supported any longer as of Django 1.7.

What I ended up doing was modifying the Django code in …/django/db/backends/creation.py, specifically the _create_test_db and _destroy_test_db functions.

For _create_test_db I commented out the cursor.execute("CREATE DATABASE ... line and replaced it with pass so the try block wouldn’t be empty.

For _destroy_test_db I just commented out cursor.execute("DROP DATABASE – I didn’t need to replace it with anything because there was already another command in the block (time.sleep(1)).

After that my tests ran fine – though I did set up a test_ version of my regular database separately.

This isn’t a great solution of course, because it will break if Django is upgraded, but I had a local copy of Django due to using virtualenv so at least I have control over when/if I upgrade to a newer version.

Another solution not mentioned: this was easy for me to implement because I already have multiple settings files (for local / staging / production) that inherit from base.py . So unlike other people I did not have to overwrite DATABASES[‘default’], as DATABASES isn’t set in base.py

SimpleTestCase still tried to connect to my test database and run migrations. When I made a config/settings/test.py file that didn’t set DATABASES to anything, then my unit tests ran without it. It allowed me to use models that had foreign key and unique constraint fields. (Reverse foreign key lookup, which requires a db lookup, fails.)

(Django 2.0.6)

PS code snippets

PROJECT_ROOT_DIR/config/settings/test.py:
from .base import *
#other test settings

#DATABASES = {
# 'default': {
#   'ENGINE': 'django.db.backends.sqlite3',
#   'NAME': 'PROJECT_ROOT_DIR/db.sqlite3',
# }
#}

cli, run from PROJECT_ROOT_DIR:
./manage.py test path.to.app.test --settings config.settings.test

path/to/app/test.py:
from django.test import SimpleTestCase
from .models import *
#^assume models.py imports User and defines Classified and UpgradePrice

class TestCaseWorkingTest(SimpleTestCase):
  def test_case_working(self):
    self.assertTrue(True)
  def test_models_ok(self):
    obj = UpgradePrice(title='test',price=1.00)
    self.assertEqual(obj.title,'test')
  def test_more_complex_model(self):
    user = User(username='testuser',email='hi@hey.com')
    self.assertEqual(user.username,'testuser')
  def test_foreign_key(self):
    user = User(username='testuser',email='hi@hey.com')
    ad = Classified(user=user,headline='headline',body='body')
    self.assertEqual(ad.user.username,'testuser')
  #fails with error:
  def test_reverse_foreign_key(self):
    user = User(username='testuser',email='hi@hey.com')
    ad = Classified(user=user,headline='headline',body='body')
    print(user.classified_set.first())
    self.assertTrue(True) #throws exception and never gets here

When using the nose test runner (django-nose), you can do something like this:

my_project/lib/nodb_test_runner.py:

from django_nose import NoseTestSuiteRunner


class NoDbTestRunner(NoseTestSuiteRunner):
    """
    A test runner to test without database creation/deletion
    Used for integration tests
    """
    def setup_databases(self, **kwargs):
        pass

    def teardown_databases(self, old_config, **kwargs):
        pass

In your settings.py you can specify the test runner there, i.e.

TEST_RUNNER = 'lib.nodb_test_runner.NoDbTestRunner' . # Was 'django_nose.NoseTestSuiteRunner'

OR

I wanted it for running specific tests only, so I run it like so:

python manage.py test integration_tests/integration_*  --noinput --testrunner=lib.nodb_test_runner.NoDbTestRunner

You can set databases to an empty list inside the normal TestCase from django.test.

from django.test import TestCase

class NoDbTestCase(TestCase):
    databases = []