First, set up the session cookie file which will be used for fetching input. In the browser, copy the value of the session cookie for the site, which should be a long hex string, and save it in a file called session.cookie.

To run tests for all days:

npm test

To run tests for a specific day:

npm test -- -g 04

OR

npm test test/04.spec.js

To run the solution for a particular day:

bin/aoc 4

OR

npm start 4

To debug:

DEBUG=aoc bin/aoc 4