I have been doing React development for 4 years now and I have never set it up from scratch and only have a rough idea how it’s done. I still apply for react jobs and do fine. Installing something from scratch is one of the least important tests because it’s something that companies typically do once every few years, they can afford to flounder for a few days on that.

I reinstall Linux from scratch about once every 5 years, long enough that I totally forget how to do it. So I keep a file with all the commands to do it.

Exactly. Greenfield projects are exceedingly rare.

I can easily write tests for Cypress without knowing anything about react because Cypress doesn't require react. Strange filter.

https://www.cypress.io/

That may be true, but there's no justification for taking it out on the candidate.

I mean, you set up cypress exactly once, and after that you write only tests.

It seems reasonable to me to not be great at setting it up.