Cygni Graduate Trainee interview questions

I was asked to solve a "homework" assignment after a first physical interview. The assignment given is, in my opinion, cleverly designed. I learned a lot from solving it. But it's also open-ended and doesn't mention anything about for example including tests of the code. Despite that, and although the instructions didn't even mention the word "test" (or any conjugation of "test"), I was told in written feedback that I should have looked at testing using either named tools and/or that I should have mocked the network calls instead of using the actual services, which was also not asked about. On the good side, I learned a lot from doing the exercise. On the bad side, the company didn't bother to meet me for a technical interview, where I would have had the opportunity to explain my solution, which in some respects is more advanced than what is asked for in the written instructions. Given the time and effort I spent solving and presenting a fully functioning solution, I was very disappointed that they didn't allow me to present it in a physical meeting.