removal of testresources from setup.cfg has broken this dependency for oslo.db 4.34

this is an issue that keeps coming up, for example at https://bugs.launchpad.net/keystone/+bug/1572202.

oslo.db is in this funny position where it is not only a library that other projects use for database access, it is also a library that is used to support running test suites. And as such, it includes modules within its normal library functions that themselves are dependencies on test-oriented libraries like testresources and testscenarios.

This implies that oslo.db really needs to have testresources and testscenarios in its normal requirements.txt, but for whatever reason, they keep getting removed. For a long time they found themselves in setup.cfg within the "test" section which seemed to fix things but then in https://review.openstack.org/#/c/550842/ this was removed again and we are broken again.

To illustrate the issue:

git clone git://git.openstack.org/openstack/keystone
cd keystone
# remove oslo.db from upper-requirments so they get the latest (4.34, not 4.33)
curl https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt | grep -v "oslo.db" > upper-constraints.txt
TOX_TESTENV_PASSENV="UPPER_CONSTRAINTS_FILE" UPPER_CONSTRAINTS_FILE=upper-constraints.txt tox -v -r --pre -e py27 -- 'keystone.tests.unit.*sql.*'

output:

=========================
Failures during discovery
=========================
--- import errors ---
Failed to import test module: keystone.tests.unit.identity.backends.test_sql
Traceback (most recent call last):
  File "/home/classic/Desktop/tmp/keystone/.tox/py27/lib/python2.7/site-packages/unittest2/loader.py", line 456, in _find_test_path
    module = self._get_module_from_name(name)
  File "/home/classic/Desktop/tmp/keystone/.tox/py27/lib/python2.7/site-packages/unittest2/loader.py", line 395, in _get_module_from_name
    __import__(name)
  File "keystone/tests/unit/identity/backends/test_sql.py", line 14, in <module>
    from oslo_db.sqlalchemy import test_fixtures as db_fixtures
  File "/home/classic/Desktop/tmp/keystone/.tox/py27/lib/python2.7/site-packages/oslo_db/sqlalchemy/test_fixtures.py", line 18, in <module>
    import testresources
ImportError: No module named testresources

Failed to import test module: keystone.tests.unit.test_sql_banned_operations
Traceback (most recent call last):
  File "/home/classic/Desktop/tmp/keystone/.tox/py27/lib/python2.7/site-packages/unittest2/loader.py", line 456, in _find_test_path
    module = self._get_module_from_name(name)
  File "/home/classic/Desktop/tmp/keystone/.tox/py27/lib/python2.7/site-packages/unittest2/loader.py", line 395, in _get_module_from_name
    __import__(name)
  File "keystone/tests/unit/test_sql_banned_operations.py", line 22, in <module>
    from oslo_db.sqlalchemy import test_fixtures as db_fixtures
  File "/home/classic/Desktop/tmp/keystone/.tox/py27/lib/python2.7/site-packages/oslo_db/sqlalchemy/test_fixtures.py", line 18, in <module>
    import testresources
ImportError: No module named testresources

Failed to import test module: keystone.tests.unit.test_sql_upgrade
Traceback (most recent call last):
  File "/home/classic/Desktop/tmp/keystone/.tox/py27/lib/python2.7/site-packages/unittest2/loader.py", line 456, in _find_test_path
    module = self._get_module_from_name(name)
  File "/home/classic/Desktop/tmp/keystone/.tox/py27/lib/python2.7/site-packages/unittest2/loader.py", line 395, in _get_module_from_name
    __import__(name)
  File "keystone/tests/unit/test_sql_upgrade.py", line 53, in <module>
    from oslo_db.sqlalchemy import test_fixtures as db_fixtures
  File "/home/classic/Desktop/tmp/keystone/.tox/py27/lib/python2.7/site-packages/oslo_db/sqlalchemy/test_fixtures.py", line 18, in <module>
    import testresources
ImportError: No module named testresources

solution:

testresources and testsceanrios need to be in requirements.txt, *not* test-requirements.txt.