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Capture and make assertions on transaction.on_commit() callbacks.

Project description

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Capture and make assertions on transaction.on_commit() callbacks. This allows you to write your tests with the TestCase, rather than needing the slower TransactionTestCase to actually commit the transactions.

This package was made as a first pass for Django PR #12944, which is a solution for Ticket #30457 “on_commit should be triggered in a TestCase”. The PR has been merged to Django and has been released in version 3.2, so this package can now be considered a backport.

Read more in my blog post The Fast Way to Test Django transaction.on_commit() Callbacks.

Installation

Use pip:

python -m pip install django-capture-on-commit-callbacks

Requirements

Python 3.6 to 3.9 supported.

Django 2.2 to 3.2 supported.

Note: This package is not needed on Django 3.2+ and a system check will trigger an error on such versions.


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API

capture_on_commit_callbacks(*, using="default", execute=False)

Acts as a context manager that captures on_commit callbacks for the given database connection. It returns a list that contains, on exit of the context, the captured callback functions. From this list you can make assertions on the callbacks or call them to invoke their side effects, emulating a commit.

All arguments must be passed as keyword arguments.

using is the alias of the database connection to capture callbacks for.

execute specifies whether to call all the callbacks automatically as the context manager exits, if no exception has been raised.

For example, you can test a commit hook that sends an email like so:

from django.core import mail
from django.test import TestCase
from django_capture_on_commit_callbacks import capture_on_commit_callbacks


class ContactTests(TestCase):
    def test_post(self):
        with capture_on_commit_callbacks() as callbacks:
            response = self.client.post(
                "/contact/",
                {"message": "I like your site"},
            )

        self.assertEqual(response.status_code, 200)

        self.assertEqual(len(callbacks), 1)
        # Execute the callback
        callbacks[0]()

        self.assertEqual(len(mail.outbox), 1)
        self.assertEqual(mail.outbox[0].subject, "Contact Form")
        self.assertEqual(mail.outbox[0].body, "I like your site")

The same test can be written a bit more succinctly with execute=True:

from django.core import mail
from django.test import TestCase
from django_capture_on_commit_callbacks import capture_on_commit_callbacks


class ContactTests(TestCase):
    def test_post(self):
        with capture_on_commit_callbacks(execute=True) as callbacks:
            response = self.client.post(
                "/contact/",
                {"message": "I like your site"},
            )

        self.assertEqual(response.status_code, 200)

        self.assertEqual(len(callbacks), 1)

        self.assertEqual(len(mail.outbox), 1)
        self.assertEqual(mail.outbox[0].subject, "Contact Form")
        self.assertEqual(mail.outbox[0].body, "I like your site")

TestCaseMixin

A mixin class to be added to your custom TestCase subclass. It adds one method, captureOnCommitCallbacks() that aliases capture_on_commit_callbacks(), to match the camelCase style of unittest assertions.

You can add to your custom TestCase classes like so:

from django import test
from django_capture_on_commit_callbacks import TestCaseMixin


class TestCase(TestCaseMixin, test.TestCase):
    pass

You could then rewrite the above tests with your custom TestCase class like so:

from django.core import mail
from example.test import TestCase


class ContactTests(TestCase):
    def test_post(self):
        with self.captureOnCommitCallbacks(execute=True) as callbacks:
            response = self.client.post(
                "/contact/",
                {"message": "I like your site"},
            )

        self.assertEqual(response.status_code, 200)

        self.assertEqual(len(callbacks), 1)

        self.assertEqual(len(mail.outbox), 1)
        self.assertEqual(mail.outbox[0].subject, "Contact Form")
        self.assertEqual(mail.outbox[0].body, "I like your site")

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