A couple of schedules have appeared in the timetable database for what look like test trains for the Huyton to Wigan line (and also the curve to Bamfurlong Junction) on this coming Monday and Tuesday evenings.
Realtime Trains is the best place to find details, see U03681 and U03682.
Hopefully this will be MENTOR, in which case we can hope for test 319s soon. I don't suppose we'll see any passenger workings until May, but you never know.
Update: Having just observed it at Huyton I can confirm that Monday's train was indeed an electrification test coach, running pantograph up. Power was 97301 and 97303, top and tail.
Update: These tests were followed by 319 test runs overnight on Wednesday and Thursday nights. I don't know if all the paperwork has been signed off yet, but basically the Wigan line is now operational.