When the ‘towncrier’ library is installed at upstream version “25.8.0” or
later, the ‘sphinxcontrib-towncrier’ test suite fails; the
‘tests/_towncrier_test.py::test_towncrier_config_section_missing’ test case
fails.

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You can see this failure in the “experimental” suite:
<URL:https://ci.debian.net/packages/s/sphinxcontrib-towncrier/unstable/amd64/71705956/>

The migration of ‘src:towncrier/25.8.0-1’ is blocked by this test suite
regression; I am marking this bug as blocking bug#1136347.

This test case failure is because the test case is incompatible with recent
changes in ‘towncrier’.

The upstream ‘sphinxcontrib-towncrier’ project has addressed this bug in
recently released version “0.5.0a0”, available at
<URL:https://pypi.org/project/sphinxcontrib-towncrier/0.5.0a0/>.