TestCase failing when using transaction.atomic() inside test

[Uri Kogan]

Hello,

I am using TestCase and trying to create an object during test.

There is a log activated on MySQL server, so I see all the queries being executed there.

This "transaction.atomic" sets a SAVEPOINT in the database thinking that the transaction is already started. The problem is that there is no "TRANSACTION START". So, when exiting "with transaction.atomic()" block the whole thing crashes with "SAVEPOINT xxx DOES NOT EXIST"

The following states that TestCase "tests within two nested atomic() blocks", so it should execute "TRANSACTION START"

https://docs.djangoproject.com/en/3.0/topics/testing/tools/#django.test.TestCase

   

from django.contrib.auth.models import User

from django.test import TestCase

class FooTest(TestCase):

    def test_bar(self):

        with transaction.atomic():

            user = User.objects.create_user(username="abc", password="pass")

[Aldian Fazrihady]

I don't think the subclass of TestCase need to use transaction.atomic. Why can't you just remove the transaction.atomic? 

Regards,

Aldian Fazrihady
http://aldianfazrihady.com

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[Uri Kogan]

While this can be done in my code, there are libraries that the project use that have "transaction.atomic" in them. For example, pretty popular django-role-permissions.

From what I see in the documentation, there should be no problem to use transactions within transactions in TestCase.

On Tuesday, May 12, 2020 at 12:34:50 AM UTC+3, Aldian Fazrihady wrote:

I don't think the subclass of TestCase need to use transaction.atomic. Why can't you just remove the transaction.atomic? 

Regards,

Aldian Fazrihady
http://aldianfazrihady.com

Pada tanggal Sel, 12 Mei 2020 04.02, Uri Kogan <urk...@gmail.com> menulis:

Hello,

I am using TestCase and trying to create an object during test.

There is a log activated on MySQL server, so I see all the queries being executed there.

This "transaction.atomic" sets a SAVEPOINT in the database thinking that the transaction is already started. The problem is that there is no "TRANSACTION START". So, when exiting "with transaction.atomic()" block the whole thing crashes with "SAVEPOINT xxx DOES NOT EXIST"

The following states that TestCase "tests within two nested atomic() blocks", so it should execute "TRANSACTION START"

https://docs.djangoproject.com/en/3.0/topics/testing/tools/#django.test.TestCase

   

from django.contrib.auth.models import User

from django.test import TestCase

class FooTest(TestCase):

    def test_bar(self):

        with transaction.atomic():

            user = User.objects.create_user(username="abc", password="pass")

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[Aldian Fazrihady]

When testing django apps, my unit test usually accesses the django app via django test client: https://docs.djangoproject.com/en/3.0/topics/testing/tools/#the-test-client.
Django test client simulates http access, so my Django tests always run my Django code starting from Django views. 
Even though there must be many django app code that has `transaction.atomic` inside it, I never need to add `transaction.atomic` in my unit test code.
If I need to simulate initial state by having some data inserted to database, I did that either using factoryboy or django ORM framework, but I see no point to add `transaction.atomic` to that data initialization code.

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[Uri Kogan]

That not that simple in my case because. I'll show what I mean:

from django.contrib.auth.models import User

from django.test import TestCase
from rolepermissions.roles import assign_role

class FooTest(TestCase):

    def test_bar(self):

        u = User.objects.create_user(username="abc", password="pass")

        assign_role(u, "role_admin")
        retrieve_and_analyze_view_using_u_credentials()

I am testing that my permission routines work by creating a user, assigning permissions to the user, retrieving the view and analyzing it. That "assign_role" call of django-role-permissions uses "transaction.atomic". Which, of course, I would not want to change, as this is an external library.

So I can't really remove usages of "transaction.atomic"

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[Aldian Fazrihady]

Probably you need to use TransactionTestCase, which is the parent of TestCase instead: https://docs.djangoproject.com/en/3.0/topics/testing/tools/#transactiontestcase
That page also mentions a specific problem when using transaction on TestCase:
```
A consequence of this, however, is that some database behaviors cannot be tested within a Django TestCase class. For instance, you cannot test that a block of code is executing within a transaction, as is required when using select_for_update(). In those cases, you should use TransactionTestCase.
111

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[Uri Kogan]

The documentation states that "you cannot test that a block of code is executing within a transaction" while I am looking to "test a block of code that has a transaction".

In any case, the issue here is that "transaction.atomic" does not work when nested while it should clearly work.

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[Uri Kogan]

Continuing my investigation I got the a following which does not work but should:

from django.contrib.auth.models import User

from django.test import TransactionTestCase

from django.db import transaction

class FooTest(TransactionTestCase):

    def test_bar(self):

        with transaction.atomic():

            with transaction.atomic():

                u = User.objects.create_user(username="abc", password="pass")

                print("created user: {}".format(u.username))

The crash of "SAVEPOINT does not exist" occurs when exiting inner `transaction.atomic' block.