Speeding up Django unit tests with SQLite, reuse-db and RAMDisk

Recently, Harry wrote a post about how to speed up Django unit-testing by using a persistent in-memory SQLite database.

While Harry uses the default Django testrunner and a Linux machine, I use pytest with pytest-django on a Mac. This changes a few things, and this post will show the differences. So it's very specific to:

  • Django
  • pytest
  • macOS

Create and mount the RAMDisk

/dev/shm is a Linux thing. But Harry already provided the link to a working solution on Stack Overflow to how to do this on macOS.

$ hdiutil attach -nomount ram://$((2 * 1024 * SIZE_IN_MB))
/dev/disk2

$ diskutil eraseVolume HFS+ RAMDisk /dev/disk2

This creates an in-memory Volume that can store the persistent SQLite database.

Use SQLite

Maybe I'm doing this all wrong, but because I use pytest, I configure the test database in a separate configuration file like this.

# config/settings/testing.py
from .common import *

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': ':memory:',
        'TEST': {}
    }
}

Use it in-memory

What --keepdb is for the default testrunner, --reuse-db is for pytest-django. I usually set this as the default for all test runs in pytest.ini.

# pytest.ini
[pytest]
DJANGO_SETTINGS_MODULE=config.settings.testing
addopts = --reuse-db

To not re-use the database, pytest-django's argument is --create-db. So Harry's

if 'keepdb' in sys.argv:

becomes

if not 'create-db' in sys.argv:

in my case. To use the RAMDisk:

# config/settings/testing.py

[...]

import sys
if not 'create-db' in sys.argv:
    # and this allows you to use --reuse-db to skip re-creating the db,
    # even faster!
    DATABASES['default']['TEST']['NAME'] = '/Volumes/RAMDisk/myfunnyproject.test.db.sqlite3'

When there's no RAMDisk

If there is no RAMDisk, for example after a reboot, then the test run fails as soon as it hits the database. Obviously.

>       conn = Database.connect(**conn_params)
E       django.db.utils.OperationalError: unable to open database file

I just throw another if statement in there to check for the existence of the RAMDisk.

if os.path.isdir('/Volumes/RAMDisk') and not 'create-db' in sys.argv:

Summary

You can check a full test configuration here:

https://github.com/FlowFX/unkenmathe.de/blob/master/src/config/settings/testing.py