#25251: Inconsistent availability of data from migrations in TestCases when
using
--keepdb
-------------------------------------+-------------------------------------
Reporter: David Szotten | Owner: Romain
| Garrigues
Type: Bug | Status: new
Component: Testing framework | Version: 1.8
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 1
Easy pickings: 0 | UI/UX: 0
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Comment (by Markus Holtermann):
A few more insights in what's happening:
1. The issue occurs when ` TransactionTestCase`s are involved.
2. Data will be unavailable even in regular `TestCase`s.
Let's assume an empty database. Additionally, the database must support
transactions (e.g. PostgreSQL or MySQL (but not `MyISAM`)). Let's further
say you have two test classes (`TestRegular(TestCase)` and
`TestTx(TransactionTestCase)`) with the test methods `TestRegular.test_1`
and `TestTx.test_2`.
* When you run `manage.py test --keepdb` for the first time, Django will
apply all migrations. That means, data created within those migrations
will be present.
* Django runs tests inheriting from `TestCase` before those inheriting
from `TransactionTestCase`
(https://github.com/django/django/blob/9bf5e9418f425666726559c9f1981a516da30aab/django/test/runner.py#L632
and
https://github.com/django/django/blob/9bf5e9418f425666726559c9f1981a516da30aab/django/test/runner.py#L807-L832).
That means, `test_1()` will be run before `test_2()`.
* When data should be serialized for a database, Django will insert that
data during the setup for a test function
(https://github.com/django/django/blob/9bf5e9418f425666726559c9f1981a516da30aab/django/test/testcases.py#L1005-L1012).
This can be enabled explicitly for `TransactionTestCase` using
`serialized_rollback=True`
(https://docs.djangoproject.com/en/3.1/topics/testing/overview/#rollback-
emulation)
* When a test function in a `TransactionTestCase` is over, Django executes
the `flush` management command
(https://github.com/django/django/blob/9bf5e9418f425666726559c9f1981a516da30aab/django/test/testcases.py#L1063-L1066).
This empties the database.
* At the end of the test suite, however, Django does _not_ reinsert
serialized test data, leaving the database empty after the first
`--keepdb` run.
* Running `manage.py test --keepdb` again means, the database is empty
(has no data that was previously created by the migrations). This means,
tests in regular `TestCase`s (e.g. `test_1()` will now fail as well.
--
Ticket URL: <https://code.djangoproject.com/ticket/25251#comment:38>
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