Is there's a Test and Go in Chiang Mai?

Yes there is. Its called Sandbox. It’s almost the same as the Test & Go in Bangkok. But you have to stay in Chiang Mai for at least 7 days. Better choose the Test & Go package in Bangkok after 1 day and with a negative PCR test you can go wherever you want with the exception of certain provinces. 
https://www.thaiembassy.com/travel-to-thailand/chiang-mai-sandbox

36 minutes ago, Moneyhonour said:

Yes there is. Its called Sandbox. It’s almost the same as the Test & Go in Bangkok. But you have to stay in Chiang Mai for at least 7 days. Better choose the Test & Go package in Bangkok after 1 day and with a negative PCR test you can go wherever you want with the exception of certain provinces. 
https://www.thaiembassy.com/travel-to-thailand/chiang-mai-sandbox

You quoted a commercial site with outdated info.

Sandbox and test&go are two different things, they apply the same all over the places which receive direct flights from abroad. The fact is at the moment Chiang Mai has only occasional international direct flights (e.g. Korea).

If your flight to Chiang Mai is via Bangkok, test&go is done in Bangkok.