Speeding up Django Testing

Im looking to learn more about your testing flows with Django.

Background information http://docs.djangoproject.com/en/dev/topics/testing/

Im encountering difficulties when using test driven development. The test runner of Django constantly creates all db models in a test db when starting. For our current projects (between 40 and 240 models) this means it takes easily 20s for tests to start.

This makes it completely unworkable for testing a new feature often. My question, how do you guys work around this?

I've tried a few things in the past a.) - change the testloader to reuse the same test db every time and apply migrations when needed b.) - run my unit tests from within the __main__ flow of python files

option b is awkward with the sys.path, option a is doable but doesnt seem to be the dj开发者_StackOverflow中文版ango way.

Update: Option A is indeed not such a bad solution. Its just quite a bit of effort. Which makes me believe people use a different workaround. SQL lite could be that workaround. But im guessing there are more.

---

change the testloader to reuse the same test db every time and apply migrations when needed

1. I don't see anything wrong in writing your own test runner that merely truncates the tables instead of dropping and creating the database. This is djangoic in that it solves a specific problem. There is a ticket open for allowing grouping of test cases into test suites. Once it is fixed you should be able to group your test cases into suites for easier management. You can also inspect the patch attached to the ticket and see if it will suit your purpose.

2. As Ned suggested you can use an in memory database. This depends to a large extent on your data model and queries being portable across databases.

3. If you haven't already try to reorganize your test cases. In my experience not all test classes need to sub class django.test.TestCase. Find out those test classes that can do with sub classing unittest.TestCase. This will speed up things a little bit.

4. Reorganize fixtures. Move common fixtures to a single file and load it before the test run rather than inside each test class (using fixtures = [...]).

---

Using an in-memory SQLite database during testing definitely speeds things up.

---

I don't like the idea of using a different database (SQLite) for testing, so my unit tests use the same database as the production application - postgres.

Out of the box, this makes creating/destroying the database the slowest step in running tests.

Django 1.8 will solve this problem with the --keepdb flag

But we're still not there yet, so we must make do with other means.

Solution 1) Use pytest-django

You can use that to make your tests run without re-creating the database. It works. If you only care about running tests on the command line, I suggest this.

In my case, I like to use the PyCharm IDE, and being able to run tests by right clicking files/methods is definitely a plus for me, so I had to go with...

Solution 2) The TEST_MIRROR trick.

In your settings.py file, configure your database like:

if os.getenv('USE_TEST_DB') == '1':
    DATABASES = {
        'default': {
            'ENGINE': 'django.db.backends.postgresql_psycopg2',
            'NAME': 'mydbtesting',
            'USER': 'mydb',
            'PASSWORD': 'mydb',
            'HOST': 'localhost',
            'PORT': '5432',
            'TEST_MIRROR': 'default',
        }
    }
else:
    DATABASES = {
        'default': {
            'ENGINE': 'django.db.backends.postgresql_psycopg2',
            'NAME': 'mydb',
            'USER': 'mydb',
            'PASSWORD': 'mydb',
            'HOST': 'localhost',
            'PORT': '5432',
        }
    }

So, "mydb" is the database that will be used for normal execution and "mydbtesting" is for tests.

The TEST_MIRROR setting is not actually meant for this, but the fact is that if you run tests with a database configured like that, Django will not re-create/destroy which is what we want.

But first we have to create that database with something like:

export USE_TEST_DB=1
./manage.py syncdb --migrate

Then whenever you want to run tests fast, just set the USE_TEST_DB environment variable to '1'. To get same benefit on Pycharm, you can go to Run/Debug Configurations, Defaults / Django tests, then on Environment variables, add USE_TEST_DB = 1

---

UPDATE:

Sample application is on Github: https://github.com/freedomsponsors/www.freedomsponsors.org/blob/099ec1a7a1c404eba287d4c93d58c8cf600b2769

---

I have found another way to speed up the testing. If your test models are auth users (User model), and you set a password for them, the hashing function takes a decent number of milliseconds to finish. What I do is add this to my test settings:

PASSWORD_HASHERS = (
    'django.contrib.auth.hashers.MD5PasswordHasher',
)

This enforces MD5 hashing for password which is much faster than the default one. In my case, this improved 12 tests, each creates 7 users, from 4.5 seconds to 500 ms.

Be careful not to add this to your production settings!

---

You can run only tests that interest you specyfically, look here: http://docs.djangoproject.com/en/dev/topics/testing/?from=olddocs#running-tests

Like in this example - run just specyfic TestCase:

$ ./manage.py test animals.AnimalTest

As for the test database - it is created and destroyed each time the test runs :( Also for testing you could use sqlite database if it is possible in your workflow.

---

As of Django 1.8, you can keep the test database around so that you don't rebuild it every time you test. Just add the --keepdb flag.

python manage.py test --keepdb

Exclude the --keepdb flag to rebuild the test database from scratch.

---

I have found another way to speed up testing. The most time consuming operation is writing to/reading from hard drive (I'm using sqlite for testing). The solution is to create ramdisk, and put the sqlite database file there. I have reduced testing time by factor of 10.

Creating ramdisk:

#!/bin/sh

mkdir -p /tmp/ramdisk; chmod 777 /tmp/ramdisk
mount -t tmpfs -o size=256M tmpfs /tmp/ramdisk/

Changing db file path:

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': '/tmp/ramdisk/test.db',
        'TEST_NAME': '/tmp/ramdisk/test.db',
    }
}

---

Here is simple test tools that provides no-reload database along with signals so you don't need to care about test database https://github.com/plus500s/django-test-tools