the test_output_order "check" is racy.

 (CK_FORK=no GST_CHECK=test_output_order make elements/multiqueue.forever).

The problem is indeed the test and not the actual element behaviour.

The objects to push are being pulled out of the single internal queues in the right order and at the right time...

But between:
* the moment the global multiqueue lock is released (which was used to detect if we should pop and push downstream the next buffer)
* and the moment it is received by the source pad (which does the check)

=> another single queue (like the unlinked pad) might pop and push a buffer downstream

What should we do ? Putting a bigger margin of error (say 5 buffers) doesn't help, it'll eventually fail.

I can't see how we can detect this reliably.