Major - P3 Topology.close() closes all Servers but Topology._ensure_opened() only re-opens Servers if the Topology is already open. It takes two calls to Topology._ensure_opened() to actually re-open each Server.
Topology._ensure_opened() should always re-start the monitor thread for each server. This issue is causing test_replica_set_reconfig.TestSecondaryAdded.test_client to fail with:
FAILURE: Didn't ever reconnect to both secondaries (AssertionError) Traceback (most recent call last): File "/data/mci/4aeb438114e1a8e42f509d2e3edab21a/src/test/test_replica_set_reconfig.py", line 160, in test_client 'reconnect to both secondaries') File "/data/mci/4aeb438114e1a8e42f509d2e3edab21a/src/test/utils.py", line 309, in wait_until raise AssertionError("Didn't ever %s" % success_description) AssertionError: Didn't ever reconnect to both secondaries