added test to check tryToResolveConflict log output

src/ZODB/tests/testconflictresolution.py

@@ -292,6 +292,75 @@ And load the pickle:
     >>> db2.close()
     """
 
+def show_tryToResolveConflict_log_output():
+    """
+    Verify output generated by tryToResolveConflict in the logs
+
+    >>> db = ZODB.DB('t.fs') # FileStorage!
+    >>> storage = db.storage
+    >>> conn = db.open()
+    >>> conn.root.x = ResolveableWhenStateDoesNotChange()
+    >>> conn.root.x.v = 1
+    >>> transaction.commit()
+    >>> serial1 = conn.root.x._p_serial
+    >>> conn.root.x.v = 2
+    >>> transaction.commit()
+    >>> serial2 = conn.root.x._p_serial
+    >>> oid = conn.root.x._p_oid
+
+Install a log handler to be able to show log entries
+
+    >>> import logging
+    >>> from zope.testing.loggingsupport import InstalledHandler
+    >>> handler = InstalledHandler('ZODB.ConflictResolution',
+    ...     level=logging.DEBUG)
+
+We conflict if both the committed and new are different than the original:
+
+    >>> p = storage.tryToResolveConflict(
+    ...         oid, serial2, serial1, storage.loadSerial(oid, serial2))
+    ... # doctest: +ELLIPSIS
+    Traceback (most recent call last):
+    ...
+    ConflictError: database conflict error (oid 0x01, ...
+
+If content doesn't support conflict resolution:
+
+    >>> conn.root.y = Unresolvable()
+    >>> conn.root.y.v = 1
+    >>> transaction.commit()
+    >>> oid = conn.root.y._p_oid
+    >>> serial = conn.root.y._p_serial
+
+    >>> p = storage.tryToResolveConflict(
+    ...         oid, serial, serial, storage.loadSerial(oid, serial))
+    ... # doctest: +ELLIPSIS
+    Traceback (most recent call last):
+    ...
+    ConflictError: database conflict error (oid 0x02, ...
+
+Let's see what went into the log:
+
+    >>> len(handler.records)
+    2
+
+    >>> import six
+
+    >>> msg = handler.records[0]
+    >>> six.print_(msg.name, msg.levelname, msg.getMessage())
+    ZODB.ConflictResolution ERROR Unexpected error
+
+    >>> msg = handler.records[1]
+    >>> six.print_(msg.name, msg.levelname, msg.getMessage())
+    ZODB.ConflictResolution DEBUG Conflict resolution failed with ConflictError: database conflict error
+
+Cleanup:
+
+    >>> handler.uninstall()
+    >>> db.close()
+    """
+
+
 def test_suite():
     return unittest.TestSuite([
         manuel.testing.TestSuite(