[Fixed]-Django.db.utils.InterfaceError: connection already closed failures when updating to Django 3.0

I ran into this as well. It appears to be a bug in pytest-django. Here’s the relevant issue. There’s an open PR to resolve it. If it’s a big enough inconvenience you can use the branch in that PR or pin your dependencies to an earlier version.

We were hitting the same issue, and upgrading from Django 3.0.2 to Django-3.0.4 resolved it. There are several DB related fixes in those two versions, but I don’t know which one solved our problem.

Just a forward note, it’s near impossible to provide more information than already is in the stacktrace. However, you can investigate:

• Check when the connection get closed and by which test (run them individually via script for example).
• For tests that fail, check the code for deprecated parts of Django (searching for things that were removed/deprecated between 2.3 and 3.0).
• Run a linter to see if someone changed a private variable inside of Django framework as workaround.
• Check the transactions of postgres.

Then once you have which part of the code has the error narrow it down by creating smaller failing tests.

I had the same issue using pytest.

Downgrading from 5.4.1 to 5.3.5 fixed it.

All these issues occur because of the incompatibility of the other packages with django 3.0
when i ran into this error i updated my requirement.txt file manually and then intalled all the requirements using pip in the same env.

In my case I just forgot to run python manage.py makemigrations.