test/mean.test.js

import { test } from "node:test";
import assert from "node:assert/strict";
import { mean } from "../src/mean.js";

test("mean of multiple positive numbers", () => {
  assert.strictEqual(mean([1, 2, 3, 4]), 2.5);
});

test("mean of single-element array", () => {
  assert.strictEqual(mean([42]), 42);
});

test("mean with negative and mixed numbers", () => {
  assert.strictEqual(mean([-2, 0, 4, 8]), 2.5);
});

test("mean of empty array returns NaN", () => {
  assert.ok(Number.isNaN(mean([])));
});

test("mean returns NaN when any element is invalid", () => {
  assert.ok(Number.isNaN(mean([1, 2, NaN])));
  assert.ok(Number.isNaN(mean([1, "2", 3])));
});