Here is a library chock full of bugs. It is your job, intrepid programmer, to squash them.
Fork the repo and get it on your machine.
Do an npm install.
Now run npm run test:easy and behold the litany of errors.
Take a look in challenges > easy and try to fix some code. Run npm run test:easy again to see if it works!
Keep going until you have fixed the easy bugs.
The challenges in medium and hard will require you to look things up (some links are included to help). You can npm run test:medium and npm run test:hard to check your progress.