Before the design of the WZ series, also known as the Warhawk series of engines, the only domestic independently-designed turbofan engine was the Kunlun, with no other engines to compare with. Consequently, the engine development process and progress could only be benchmarked against the Kunlun engine.
The "aircraft flight tests" of the Kunlun engine were conducted two years after the completion of the first prototype assembly.
At that time, the Kunlun was already capable of functioning normally. It had no serious problems during regular power operation, though it had not undergone many high-power operation tests, and its stability still needed to be strengthened further. However, all operational parameters were normal when it ran. The "aircraft flight tests" represented a new milestone and the entry into a new phase. In fact, they were also intended to perfect the design, as flight testing could help detect more issues.