I would agree with
@Yasser76 that a line exists in china. That is why all prototypes get built in China. However I do not think there is any need to waste bandwidth over it .
A
Only last year Chinese line produced B versions and Block III Prototype, this was even confirmed by head of PAC
All the prototypes were made under small scale production. You don't need a production line for that. In fact you don't use a production line for that even if you have it. The prototyping phase needs to be agile due to the frequent changes in design. A production line, otoh, is completely rigid. That is exactly the reason why the design is frozen before production for a certain number of units. Be it aircraft, cars, or bicycles. That is also how aircraft can have prototypes built without ever receiving any orders. It would also not make any sense to build an entire production line for a hand full of units.
Furthermore, you can't just have a production line sitting there without producing anything. It is a massive waste of resources and costs. If China is not producing JF-17s then they have no production line there.