Hi, Nova has tests that are using the oslo.messaging FakeDriver implementation by providing the 'fake://' transport url. The FakeExchangeManager keeps a class level dict of FakeExchange objects keyed by the communication topic[1]. This can cause that an RPC message sent by a test case is received by a later test case running in the same process. I did not find any proper way to clean up the FakeExchangeManager at the end of each test case to prevent this. To fix the problem in the nova test I did a hackish cleanup by overwriting FakeExchangeManager._exchanges directly during test case cleanup [2]. Is there a better way to do this cleanup? Cheers, gibi [1] https://github.com/openstack/oslo.messaging/blob/0a784d260465bc7ba878bedeb5c... [2] https://review.openstack.org/#/c/637233/1/nova/tests/fixtures.py