Looks like BART will get the signoff next week (before March) and will run 8-10 weeks of practice. As of today (19 Feb) it still belongs to Tutor-Saliba.
One "urban legend" I heard was that, every time there was a glitch on the people mover, the workers on BART got sent to other sites and took advantage of the people mover delay. When the people mover started up again, then they came back. Apparently, Tutor-Saliba has a number of jobs running in California, and moving people around improves teh cash flow, by making important milestones, before the ends of months.
It seems the same thing happened on BART - whenever some part was late coming, or a glitch happened, and BART slowed down, Bombardier pulled people off the people mover. For a long time, the idea was to open both pieces with one big shindig. So, when one slowed down, the other did also.
When Dublin opened up five years ago, they did 10 weeks of testing. Actually, they intended to open early, and had lots of glitches in the automatic system. BART learned a lot, and some thought they could shorten this project to a month, but, with all the exposure from accidents, power failures, etc., there's huge internal pressure to do it "by the book".
Looks like early to mid June as an opening timeframe. Despite the expected 30,000 new riders every day, the project is "revenue neutral" to BART and they have no great financial benefit by opening.