Considering it's supposed to make its world debut at the LA Auto Show in a few weeks, BMW has been very secretive about its upcoming i8 Roadster. It's been a long time coming too, as it was first revealed as a concept way back in 2012 at Beijing when it was then known as the BMW i8 Spyder. BMW hasn't released any official previews of the upcoming convertible i8 since July this year, but a new teaser video shows it undergoing production testing ahead of its debut later this month.

Shot at the Leipzig factory in Germany where the i3 hatchback and i8 coupe are assembled, the video shows the car's roof being installed. The i8 Roadster will sport a soft top, but unlike the Lamborghini Roadster it will be electrically retractable. According to reports, the i8 Roadster's fabric roof can open in 14 seconds at speeds up to 37 mph.

This of course will affect the design of the rear window, which looks a lot smaller than the coupe's in the video. The video also shows the i8 Roadster's carbon-fiber tub, aluminium frame and suspension being assembled and tested for durability. Elsewhere, the cabrio's headlights appear to have been slightly redesigned from the coupe, possibly previewing some of the mid-life facelift features that the entire range will soon receive. Other details haven't been confirmed, but rumors have suggested that the i8 Roadster will get a power boost to compensate for its extra weight.

If these rumors are to be believed, the i8 Roadster will be powered by an upgraded version of the coupe's plug-in hybrid powertrain producing around 400-hp, as well as a doubled battery capacity at 14 kWh. All will be revealed on November 28 when BMW lifts the wraps off the i8 Roadster at the LA Auto Show.