.

conftest.py

@@ -20,10 +20,32 @@
 
 from __future__ import print_function, absolute_import
 
+import pytest
+import transaction
 from golang import func, defer
 from functools import partial
 import gc
 
+# reset transaction synchronizers before every test run.
+#
+# This isolates different tests from each other. When there is failure in test A,
+# and it is not careful enough to close all ZODB Connections (but DB and
+# storage are closed), those connections will continue to participate in
+# transaction boundaries, and crash on access to closed storage.
+#
+# Fix it once and for all in one place here.
+# It would be more easy if DB.close would call conn.close for all its opened
+# connections, but unfortunately it is not the case.
+#
+# See also TestDB_Base.teardown, but it isolates only module Ma from module Mb,
+# not test M.A from test M.B.
+@pytest.fixture(autouse=True)
+def transaction_reset():
+    transaction.manager.clearSynchs()
+    yield
+    # nothing to run after test
+
+
 # Before pytest exits, teardown WCFS(s) that we automatically spawned during
 # test runs in bigfile/bigarray/...
 #

lib/testing.py

 # Wendelin. Testing utilities
-# Copyright (C) 2014-2020  Nexedi SA and Contributors.
+# Copyright (C) 2014-2021  Nexedi SA and Contributors.
 #                          Kirill Smelkov <kirr@nexedi.com>
 #
 # This program is free software: you can Use, Study, Modify and Redistribute
@@ -204,6 +204,10 @@ class TestDB_Base(object):
 
     def teardown(self):
         # close connections that test code forgot to close
+        #
+        # see also conftest.transaction_reset(), which tries to isolate all
+        # tests from each other. (TestDB_Base.teardown - on the other hand - is
+        # invoked per module and so isolates at module-level only)
         for connref, tb in self.connv:
             conn = connref()
             if conn is None: