Are they still planning not to open it until 2022? Is it the buildings they are waiting for? Obviously testing is required but persumably it is two isolated single car systems so I wouldn't of thought there were that many perturbations to test?
Well clearly it’s not finished yet - looks like a lot of the systems need to be complete (platform screen doors, ventilation, lighting, etc).
Then all the individual systems need testing, then integration testing.
Then there will be dozens of operational tests to complete. Trial evacuations in the tunnels, in the trench, on the bridge, at the station when the doors don’t open, and so on. Testing protocols for an emergency landing. What to do when the rail station or airport is closed in a hurry. Failure of the ventilation. What to do if one car is out of service unexpectedly and/or for a prolonged period. I won’t go on, but there is so much to test on a system like this, and it takes time. Then there will be a period of trial operation with everything working but no paying passengers, to shakedown everything. If I was them I’d do this for at least 2-4 weeks.