It's not that difficult to know what's going on in China. There are many millions of Chinese people who call friends and family outside the country regularly. You can go read Chinese social media. There are Westerners in China who post to Western social media. There are even many people on HN who live in China.
> if you believe their reporting the mass testing generally didn't find any cases at all
That's not true. Their mass testing typically picked up further cases, which were isolated:
* In the June 2020 Beijing outbreak, mass testing uncovered over 300 cases.[1]
* In the October 2020 Qingdao outbreak, 9 additional cases (beyond the original three) were caught by mass testing.[2] That suggests that this outbreak was detected early.
* In the October 2020 outbreak in Kashgar, over a hundred additional cases were detected through mass testing.[3]
And of course, there was a more widespread outbreak in December (still concentrated in the Northeast), which peaked at over 100 new cases a day nationwide, and which was stopped with widespread lockdowns and mass testing.
> Also, a lot of the information about the source of the outbreaks and their successful methods for eradicating Covid is really obvious propaganda.
I assume you're talking about the cold chain. I don't see how that's "obvious propaganda." There's good evidence from contact-tracing that some of the subsequent outbreaks originated in people who work in the cold chain. It may seem strange from an American or European point of view, because the cold chain is way less of a problem than the literally millions of infected people walking around in Europe and the US. But in a country with essentially zero community spread and strict quarantine at the border, much less common pathways become a concern. It only takes one person touching a contaminated package and then touching their eyes to set off a new epidemic.
1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7445627/
2. https://www.nejm.org/doi/full/10.1056/NEJMc2032361
3. https://www.bbc.com/news/world-asia-china-54687533