BERLIN — Chancellor Angela Merkel of Germany and Premier Li Keqiang of China settled into the back seat of a driverless Volkswagen van, fastened their seatbelts and went for a spin around a disused airport landing strip in central Berlin.

“There is nothing like seeing in practice what’s possible,” Ms. Merkel beamed when they returned.

That was July 2018, when economic cooperation between the two countries looked limitless — combining Germany’s powerful auto industry and China’s technology giant, Huawei.

Eighteen months later, Germany is embroiled in a tortured debate over whether to allow Huawei to help build its 5G next generation mobile network. But with German automakers, including Audi and Daimler, already working closely with Huawei, it may be China who sits in the driver’s seat.

Whatever Germany decides will shape its relations with China for years and reverberate across the Continent. It will send a powerful political signal on how united, or fractured, Europe will be in the digital age of rivalry between Washington and Beijing.