I don't think that http://bazaar.launchpad.net/~indicator-applet-developers/dbus-test-runner/trunk.12.10/revision/39.1.46 is correct.
Ignore-return is for a task to always pass regardless of its return value, and that's how dbus_test_task_passed() uses it.
But all_tasks_finished_helper() probably shouldn't look at it. If the last task(s) running are ignore-return, they'll be killed prematurely when all_tasks_finished_helper() leaves 'all_finished' as TRUE s.t. dbus_test_service_run() exits. This doesn't seem desirable and I'm not sure what 39.1.46 is for.
Found by dbusmenu's test-json exiting prematurely because all of its tasks were ignore-return. On my machine, test-json-server was exiting before test-json-client even started. Sometimes. Or not. Depending on timing issues, the phase of the moon, and the polarity of the neutron flow.
The idea was that if a task doesn't have results we care about, don't block on it. This could be used for things like mock services wouldn't have a explicit kill, but when the test is complete should be torn down.