They didn't stop testing. However the "zero new cases" reports are misleading. Various reports showed that there are a few positive testing results in Wuhan each day, but because they are asymptomatic, they are not being considered as "case".

On the positive side, it shows that Wuhan now have enough testing capacity to test almost every single one who walked in a hospital even they are seeking medical help for completely different issues.

Considering they just released they had 60 positive tests, they’re still testing.