The oslotest package can be cross-tested against its consuming projects to ensure that no changes to the library break the tests in those other projects.
Refer to the instructions in https://wiki.openstack.org/wiki/Oslo/UsingALibrary for setting up cross-test jobs in the gate.
To run the cross-tests locally, invoke the script directly, passing the path to the other source repository and the tox environment name to use:
$ cd oslo.test
$ ./tools/run_cross_tests.sh ~/repos/openstack/oslo.config py27