Trial Operations involves operational exercises being carried out to ensure the safety and reliability of the railway for public use, and to fully run the timetables. The particular thing we were testing was the evacuation operation; if a train breaks down.
So, we got on an Elizabeth Line train at Woolwich, it travelled a short distance, pretended to break down in a tunnel and we will all had to get off and walk along and get on a replacement train. That replacement train then moved off. It in turn will pretended to break down so we had to exit the second train, walk along to climb up a long 150 step staircase to ground level.
Great fun. We got a swag bag too.