Where do Russian and Chinese airliner manufacturers test their airliners?
Almost all Russian (Soviet) aircrafts were tested in the Zhukovsky Airfield (Ramenskoye Airport) near Moscow.

The Comac is building a Flight Test center at Dongying, Shandong province near the Dongying Shengli Airport. The flight test of aircrafts are expected to be carried out from here.

As Peter noted, Antonov test their aircrafts at Kiev Airport, including An 225, the largest aircraft in world.