The symlinks are for grade-scope. The only required file is the _unittest.cc file so as long as it can find it in the root directory that you submit everything works on grade-scopes end and you can still develop very easily locally. If you are working on partC of the homework for example, you just do everything in the homework/partC folder and submit this entire repo, no need to move any files around or update the symlink every time before uploading.