Reusing databases doesn't work on PostgreSQL for migrations tests

[Anssi Kääriäinen]

Running migrations tests with keepdb results in failures for the second run. To reproduce:

./runtests.py --settings=<your_postgresql_settings> --keepdb migrations
# success
./runtests.py --settings=<your_postgresql_settings> --keepdb migrations
# Lots of failures.

[Claude Paroz]

This also happens on 1.8.

[Tim Graham]

I attached a patch to get someone started. I used the following workflow:

./runtests.py --settings=test_postgres migrations --parallel=1 --noinput --keepdb --failfast
(no errors)
./runtests.py --settings=test_postgres migrations --parallel=1 --noinput --keepdb --failfast

At this point you can observe and fix the next failure. With my patch applied, the next failure I see is test_regression_22823_unmigrated_fk_to_migrated_model (migrations.test_commands.MigrateTests). It's helpful to use pgAdmin to examine the state of the test database.

After you add a possible fix for thetest, run the tests without --keepdb to clear the bad state from the database. You can then repeat these steps from the top.
./runtests.py --settings=test_postgres migrations --parallel=1 --noinput