What makes you think they didn't test it on Earth first? The Chinese report on this [1] makes this clear with more accurate verbiage: "China's space station has recently conducted experiments on extraterrestrial artificial photosynthesis technology, completing the in-orbit verification of efficient carbon dioxide conversion and oxygen regeneration processes." I think the reason you want to validate your findings in the domain that they'll be used are somewhat self evident.
I only want to point out that showing scepticism to chineese scientific claims when so few details are given is well grounded.
Microgravity is not the target environment for the technology , and it verifying its operation in microgravity feels like a very minor breakthrough compared to the tech itself.
So sending it to space is performance to show off and make headlines.
Its very important tech. If their claims are true its amazing... but doing it in orbit is not the amazing part.
China is doing alot of great research, and the idea that china is behind is laughable in many sectors. But sorting through the real science is so much harder in the noise of empty papers and puffy articles.
> "Artemis is going..."
That's quite optimistic.
[1] - https://english.news.cn/20250120/375a0de3a7fc416096799714eaf...