07 — Tests

Goal

Extend the test suite with four new cases covering every function added in this tier. Uses the same built-in node:test + node:assert/strict combo from the beginner tier — still zero new dependencies.

The test file

// todo.test.js — add these four tests below the existing beginner tests
const test = require("node:test");
const assert = require("node:assert/strict");
const { completeTodo, removeTodo, pendingTodos, formatList } = require("./todo");

test("completeTodo marks a todo done", () => {
  const out = completeTodo([{ text: "a", done: false }], 0);
  assert.equal(out[0].done, true);
});

test("removeTodo drops by index", () => {
  assert.deepEqual(
    removeTodo([{ text: "a" }, { text: "b" }], 0),
    [{ text: "b" }],
  );
});

test("pendingTodos keeps only not-done", () => {
  const out = pendingTodos([
    { text: "a", done: true },
    { text: "b", done: false },
  ]);
  assert.equal(out.length, 1);
  assert.equal(out[0].text, "b");
});

test("formatList shows [x]/[ ] markers", () => {
  assert.equal(
    formatList([
      { text: "a", done: true },
      { text: "b", done: false },
    ]),
    "1. [x] a\n2. [ ] b",
  );
});

Run the tests

node --test

Expected output (4 tests passing):

✔ completeTodo marks a todo done (Xms)
✔ removeTodo drops by index (Xms)
✔ pendingTodos keeps only not-done (Xms)
✔ formatList shows [x]/[ ] markers (Xms)
ℹ tests 4
ℹ pass 4
ℹ fail 0

What each test covers

Test	Function	Assertion
completeTodo marks a todo done	completeTodo	out[0].done === true
removeTodo drops by index	removeTodo	result equals [{ text: 'b' }]
pendingTodos keeps only not-done	pendingTodos	length 1, item is 'b'
formatList shows [x]/[ ] markers	formatList	exact string with markers

Why assert/strict?

assert.equal in strict mode uses === (no type coercion). assert.deepEqual in strict mode recursively compares object values — { text: 'b' } only passes if the structure and values match exactly.

Next steps

• Add a test for seedTodos using a mock fetch (swap the global with a function that returns a resolved Promise — no network needed).
• Wire node --test into a package.json script ("test": "node --test") and run it in CI.