I don't know a single web dev who tests on Opera anymore. I personally stopped worrying about it for any of my products when it hit 1.6% market share, and that was five years ago. They're essentially not supported by anybody, and haven't been for a long time.
... But that's never mattered, since they have always known it. And they went out of their way to make sure they rendered exactly like the dominant browser. For the longest time, they'd match Internet Explorer quirk for quirk, so if you supported that you supported Opera.
Now they see that Chrome is going to win, so they're switching to copying Chrome instead. And since Chrome has a nice drop-in "Chrome in a box" rendering engine they can use, it's going to be a lot easier to pull off this time around.
They'll continue to be the browser that nobody cares about (aside from six people who are no doubt here in this thread somewhere), but your site will probably render fine on it.
EDIT: Looks like those aforementioned Opera devotees have arrived. This comment went from 6 points and the top slot down to 1 point in the last ten minutes. Funny, since it's not actually an anti-Opera comment (or of course the sort of thing that down-votes here are usually reserved for).