trac.ticket.tests.notification.NotificationTestCase fails with sqlite on Windows

[Christian Boos]

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ERROR: test_from_author (trac.ticket.tests.notification.NotificationTestCase)
Using the reporter or change author as the notification sender
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Traceback (most recent call last):
  File "C:\projects\trac\trac\ticket\tests\notification.py", line 480, in test_from_author
    ticket.save_changes('noname', 'Final changes')
  File "C:\projects\trac\trac\ticket\model.py", line 355, in save_changes
    old_db_values.get(name), db_values.get(name)))
  File "C:\projects\trac\trac\db\util.py", line 128, in execute
    cursor.execute(query, params if params is not None else [])
  File "C:\projects\trac\trac\db\util.py", line 61, in execute
    r = self.cursor.execute(sql_escape_percent(sql), args)
  File "C:\projects\trac\trac\db\sqlite_backend.py", line 82, in execute
    result = PyFormatCursor.execute(self, *args)
  File "C:\projects\trac\trac\db\sqlite_backend.py", line 60, in execute
    args or [])
  File "C:\projects\trac\trac\db\sqlite_backend.py", line 52, in _rollback_on_error
    return function(self, *args, **kwargs)
IntegrityError: columns ticket, time, field are not unique

The reproducibility is not 100%. On 1.0-stable Python 2.6.6 and 2.7.11 both x86 and x64) were affected, but on trunk, it happened reliably with x64 builds of Python only. So it happened with both in-memory and file based SQLite databases.

I couldn't reproduce the problem locally.