If you are on macOS you may get the error UnicodeDecodeError: 'utf-8' codec can't decode byte 0xff in position 566: invalid start byte or something similar.

This error occurs because the code tester checks for all the files in the directory which includes the case#.txt files and a macOS .DS_Store file, which obviously cannot be read correctly.

You can remove this file navigating to the testcases_trains_planes directory in terminal and deleting it with rm .DS_Store

You can verify that it is removed with ls -las