For example:

https://buildbot.askmonty.org/buildbot/builders/kvm-deb-wheezy-x86/builds/1532

perfschema.setup_instruments_defaults    w1 [ fail ]

        Test ended at 2014-12-12 23:58:11

CURRENT_TEST: perfschema.setup_instruments_defaults

mysqltest: At line 82: query 'SELECT * FROM performance_schema.setup_instruments

WHERE name like "%wait/io/table/sql/handler%"' failed: 2006: MySQL server has gone away

The testcase does a server restart during the test. I believe the problem is
that it does not correctly synchronise with that server restart. It tries to
reconnect after the server has restarted. But without proper synchronisation,
the reconnect can succeed before the server has completely stopped. Then the
following queries fail as the stopping server disconnects the connection that
reconnected too early.