TaskCombine the runner from C8-05 (with describe) and assertEqual from C8-09. Implement createSortedSet() with .add, .has, .size, .toArray. Inside describe('sortedSet'), write three tests: 'starts empty', 'add then has', 'dedupes and sorts' (assertDeepEqual after adding 3,1,3,2 the toArray() is [1,2,3]). runAll() — all 3 pass.
Capstone: test a small library
275 XP15 min
Theory
Putting C8 together
Combine every C8 idea to test a real micro-library — a sorted, dedup'd integer set. You'll write the library AND the tests for it in one file.
function createSortedSet() {
const items = [];
return {
add(x) { if (!items.includes(x)) items.push(x); items.sort((a,b) => a - b); },
has(x) { return items.includes(x); },
size() { return items.length; },
toArray() { return items.slice(); },
};
}The capstone wires C8-05 runner + C8-09 better assertEqual, then writes a small suite that covers happy path, dedup, and ordering.
Why testing a library is the natural exercise
Libraries have clear inputs and outputs — perfect for tests. Plus you're going to write libraries throughout your career; learning to test them well is a permanent skill.
🔒
Sign up to start coding
Theory is open to everyone. The interactive editor, live preview, and check are unlocked with a 7-day free trial — card required, cancel anytime.
Sign up — free trial →First 15 lessons in each track are free. No card needed for those.