How to have Django test case and Selenium server use same database?

Question

I have a Django (v1.4, using Postgresql) project which I've written a bunch of working unittests for. These use FactoryBoy to generate most of their data.

I'm now starting to write some integration tests using LiveServerTestCase with Selenium. I've just realised that my tests and the live test server use different databases. Which means that data created by factories in my tests aren't available to Selenium.

I'm not sure of the best way to progress. I think I could use fixtures to supply data that would work, although this is a pain having got this far using factories instead.

Is there a way I can continue to use factories to generate data that will work for my Selenium tests? Really I'd like my tests and LiveServerTestCase to use the same database.

Answer 1

Have you tried using sqlite as your database backend for tests?

When using an in-memory SQLite database to run the tests, the same database connection will be shared by two threads in parallel: the thread in which the live server is run and the thread in which the test case is run.

from Django docs

If you're not using anything beyond regular ORM, you might benefit from test speedups as well.

Answer 2

I found out why this happened to me, and some possible workarounds, including Ilya Baryshev's answer above.

If your test descends from Django's TestCase, and if your database supports transactions, then each test runs in its own transaction, and nobody outside (no other thread, external process, or other test) can see the objects created in the database by your test.

LiveServerTestCase uses threads, so it would suffer from this problem. So the designers made it inherit from TransactionTestCase instead of TestCase, which disables these transactions, so that changes are globally visible.

What happened to me was that I added some mixins to my test class, and one of them pulled in TestCase. This doesn't cause an error, but it silently replaces the base class of LiveServerTestCase with TestCase, which enables transactions again, causing the problem that you describe.

Ilya's SQLite memory database workaround works because Django contains code that detects when using a SQLite :memory: database that actually shares the same connection between threads, so you see your test's objects in the LiveServerThread because they're inside the same transaction. However this comes with some caveats:

It’s important to prevent simultaneous database queries via this shared connection by the two threads, as that may sometimes randomly cause the tests to fail. So you need to ensure that the two threads don’t access the database at the same time. In particular, this means that in some cases (for example, just after clicking a link or submitting a form), you might need to check that a response is received by Selenium and that the next page is loaded before proceeding with further test execution. Do this, for example, by making Selenium wait until the HTML tag is found in the response (requires Selenium > 2.13)...

https://docs.djangoproject.com/en/1.4/topics/testing/#live-test-server

In my case, once we identifier that autocommit was being turned off when the test started, and tracked down why (because we had entered TestCase code that we shouldn't have done), we were able to fix the inheritance hierarchy to avoid pulling in TestCase, and then the same database was visible from both the live server thread and the test.

This also works with Postgres databases, so it would provide a solution for velotron.