/usr/lib/python3/dist-packages/os_testr/tests/files/stestr-conf is in python3-os-testr 1.0.0-0ubuntu2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | [DEFAULT]
test_path=./tests
group_regex=([^\.]*\.)*
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