As I had no "real" experience developing and I have never written a test case before it was a bit challenging for me because the code from the first part was really simple and easy and I couldnt find a case to test. Please make sure you follow some test best practices such as TDD. This helped me to build a "testable" code. Also, don't be afraid of experimenting on new technologies during your challenge (if you are confident enough that you will have enough time).