07 Tests

Goal: verify the todo module's logic using Node's built-in test runner — no extra packages required.

node:test basics

node:test ships with Node 18+ and is fully stable in Node 26. Import test and assert from built-in modules:

const test = require("node:test");
const assert = require("node:assert/strict");

• test(name, fn) registers a test case.
• assert.equal(actual, expected) fails the test if the values differ.

Test the todo module

Create todo.test.js:

// todo.test.js
const test = require("node:test");
const assert = require("node:assert/strict");
const { addTodo, formatList } = require("./todo");

test("addTodo appends a todo", () => {
  const out = addTodo([], "buy milk");
  assert.equal(out.length, 1);
  assert.equal(out[0].text, "buy milk");
});

test("formatList numbers rows", () => {
  assert.equal(formatList([{ text: "a" }, { text: "b" }]), "1. a\n2. b");
});

test("formatList handles empty", () => {
  assert.equal(formatList([]), "No todos yet.");
});

Checkpoint

node --test todo.test.js

Expected output (3 passing):

▶ addTodo appends a todo
✔ addTodo appends a todo (Xms)
▶ formatList numbers rows
✔ formatList numbers rows (Xms)
▶ formatList handles empty
✔ formatList handles empty (Xms)

ℹ tests 3
ℹ pass 3
ℹ fail 0

All 3 tests pass — the todo module is correct.

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