If code reviews in your org are glorified "styleguide checks", then they are not really code reviews at all.

Also, if you're only getting design input at code review time, that's WWAAYY too late in the process.

Code reviews should be:

• Establishing that the code has proper test coverage (functional correctness VIA coverage, not code observation)

• Establishing that it doesn't have unintended consequences in the ** implementation** (making db calls in a loop, exposing secure information, etc)

• That the implementation is of the high-level design that was already established and agreed upon by the larger development unit.

• A opportunity to ask questions to learn from whoever wrote the code

• An opportunity for the reviewers to teach techniques that could have helped in the code

Nice, so they are hot takes :D

If the design of a code change is bad, noticing that in the PR stage is not desirable. It should be discussed before someone actually went ahead and implemented it. It can also happen if people misunderstand the architecture, but again, that should be cleared up before actually implementing a change. Code style should be enforced automatically, as should test coverage and performance. Code review is also pretty bad at finding bugs from my experience. That imo leaves very few things where code review is useful that are not nitpicking.

As for programming languages, the amount does matter for individuals and for teams/organisations. A developer who can only use a single language is not very good, and using a many different languages within the same team is not good either.

It’s not that most people are bad at it, they are just out of context.

Like, I am completely swamped with a completely different business area of the code, besides checking for obviously dumb things, what can I really tell about a diff to a very separate part of the code which I may have never worked on before, with business requirements I don’t understand as I was not part of the 10 meetings that happened between the dev of the given ticket and BAs?

But does it have to be? I haven't touched non-web GUIs since 15 years, so my perspective on this is limited. And web frontend is not what I would call a well designed system for it's current purpose.

Good questions, I could probably write a lot, but I'll try to keep it short. I usually apply TDD and there are different schools of thought within it about how to structure the development process. But no matter how exactly you do it, if you focus on writing the tests while writing your code, you won't end up with an application that you then have to figure out how to test.

what to test

Well, what is the application supposed do? That is what you test, the behaviour of the application.

So in a codebase without any tests, the first thing you should write a test for is the happy path. That will probably not be a unit test. So for the web server example, set it up in a test with a file, start it and check if it serves that file.

Then you can add tests for all the error cases and for additional functionality. You can write unit tests for individual components. The ideal places to test are interfaces with clear boundaries. Ideally you should not have to look at the code of a method to be able to write a test for it. In reality that's not always so easy, especially in existing code bases, but if you have to set up more than one mock, it tends to lead to brittle tests.

Every time you encounter a bug/issue, reproduce it in a test first. And do measure code coverage, but don't make it a target, just check for places that are lacking.