Broken tests: failUnlessRaises has been deprecated

[hacklschorsch]

failUnlessRaises has been deprecated in favor of assertRaises.

This breaks tests (see ​https://app.circleci.com/pipelines/github/tahoe-lafs/tahoe-lafs/5377/workflows/cd00a81d-54c3-43be-8041-719ea727c3f1).

Thanks @sajith for the pointer (both to the broken tests and the possible cause)!

2025-12-30 20:51:45 hacklschorsch   sajith: thanks for your link to > https://app.circleci.com/pipelines/github/tahoe-lafs/tahoe-lafs/5377/workflows/cd00a81d-54c3-43be-8041-719ea727c3f1
2025-12-30 20:53:20 hacklschorsch   Seems most failures here are due to "[...] object has no attribute 'failUnlessRaises'" - Maybe some dependency has changed?
2025-12-30 20:55:31 hacklschorsch   (in the windows builds)
2025-12-30 20:55:38 hacklschorsch   IIRC these worked until a while ago
2025-12-30 21:43:49 sajith  hacklschorsch: I am not 100% sure right now, but I think Python (unittest module maybe?) has deprecated failUnlessRaises in favor of assertRaises or something, and I suspect that we've ended up importing failUnlessRaises both from twisted.trial.unittest and stdlib unittest. Just a hypothesis. I don't have the time to check right now.

[hacklschorsch]

11 tests are failing in this ​Server 2022 CPython 3.12 test run with AttributeError: 'Complete' object has no attribute 'failUnlessRaises' (or similar).

It seems this is not a Windows problem though, but a very-recent-python-problem:

Due to some different bug, that test suite seems to not be running CPython 3.12, but 3.13.7.

[hacklschorsch]

I was able to reproduce the behavior on my NixOS development machine with a 3.13.9 CPython.

Replacing all occurrences of failUnlessRaises with assertRaises fixes this problem.

[hacklschorsch]

For posterity / maybe this helps somebody sometime, I did:

python -m venv venv-3.13.9
./venv-3.13.9/bin/pip install --editable .[test]
source venv-3.13.9/bin/activate

# Find a test to check if our upcoming work does help anything.
# I got it from the CircleCI build job test pane.
# Running this should fail:
python -m twisted.trial --rterrors allmydata.test.test_hashtree.Complete

# Fix the problem
cd src/allmydata
rg -l failUnlessRaises | xargs sed -i 's/failUnlessRaises/assertRaises/'
cd ../..

# Run test again (this time it should succeed):
python -m twisted.trial --rterrors allmydata.test.test_hashtree.Complete
# Run all tests (to check we haven't broken something else...)
python -m twisted.trial --rterrors allmydata

[hacklschorsch]

I posted a fix in ​https://github.com/tahoe-lafs/tahoe-lafs/pull/1451.

[hacklschorsch]

This also affects coverage (macos-14, 3.12) and coverage (ubuntu-22.04, 3.12).

[hacklschorsch]

The cause was a change in unittest from the Python standard library.