My memory seemed to recall that it was founded information, but looking back in this thread (page 6) there are a few posts regarding the rumours from September last year, which must have been what I was remembering.There have been trains in there but none running a regular revenue service as far as I am aware.
There has been at least one loaded test train, the folly of which has been documented on RP a year or two ago.
The siding was only connected to the main line in September last year and I don't recall seeing anything concrete () on Railpage about a test train running. Do you recall where you saw it? All I've heard is rumours about it running but no one knows much else. I asked some Qube drivers about it recently but they didn't know when it ran or who drove it.
I used to live in the area so have heard a few third-hand anecdotes from factory workers who take the above rumours as gospel as well.