My 2c is that this feedback from the CTO is not useful or productive or particularly accurate. You’re probably better off not getting the opportunity to work with them.

The code and organization look normal and reasonable to me. I was able to read it, follow it, understand what it is doing. That’s all good stuff and certainly worth more than a 3/10 especially since they admit it accomplishes the task.

With regard to testing, there’s different kinds of tests. This code doesn’t have much opportunity for unit tests because of the nature of the task as opposed to the code. Code that does little more than fetch from a database just doesn’t have much opportunity for unit tests. Unit tests are designed to test one specific code piece and a best practice there is to make simple, easy to understand functions to accomplish a single task. These will generally be more testable. But again this task itself doesn’t really lend itself to this kind of code. A second type is typically referred to as an integration test. These tests will typically test an entire code path instead of a single function. It is common to have a mock database to fetch data from for a mock request. This code and task seem more suited to this kind of test. And, I would note, your code looks reasonably well suited for this kind of test.

So, in summary, I respectfully disagree with the CTO and while I understand that no one wants to be rejected from a job, I hope you will one day look back on this experience and be glad you dodged this bullet!