While I don't subscribe to the idea that you shouldn't look at the code - it's a lot more plausible for devs because you do actually have ways to validate the code without looking at it.

E.g you technically don't need to look at the code if it's frontend code and part of the product is a e2e test which produces a video of the correct/full behavior via playwright or similar.

Same with backend implementations which have instrumentation which expose enough tracing information to determine if the expected modules were encountered etc

I wouldn't want to work with coworkers which actually think that's a good idea though