Here's a site with some photos from a subway under construction in Moscow: russos.livejournal.com/697100.html#cutid1 The extension in question is in deep tunnels and has two stations. It was supposed to be finished by May 15th, but they're not quite done enough yet, and talking about an opening date of May 31st, or even June 12th. Note that there's no 8 month testing period. In fact, it's typical to open a line 2 weeks after the first clearance train runs, which includes a 1 week testing period of pre-revenue service while the finishing touches are being put on the stations. A big difference from the lengthy time between when a line looks done and when it's open for passengers that is found in the US.
And an update on the subway construction: the clearance train ran on the night of May 24th-25th, opening was scheduled for Sunday, which is the 30th. And then was delayed until June 12th due to some important piece of equipment getting stuck at customs. I guess nobody is immune to unexpected delays.