The unit test defines a test parse element that inherit from GstBaseParse.
The test pipeline is: fakesrc ! testparse ! fakesink sync=1
Before the fix b2c05cac8 the first new test would have fail because the
pipeline would have wait doing nothing just after proceeded the seek event.
The second new test would have fail because the pipeline would have
played the media instantly just after proceeded the seek event
(like if sync was FALSE on the sink).
https://bugzilla.gnome.org/show_bug.cgi?id=777780
Should reproduce 'GStreamer-WARNING **: wrong STREAM_LOCK count 0'
warnings (with make pipelines/seek.torture or pipelines/seek.forever
anyway, since it appears to be racy).
https://bugzilla.gnome.org/show_bug.cgi?id=670846
