How I write High Quality Unit tests - https://youtu.be/naL7-XQ7T70

unit-testing.js

/**
 * Returns a list of numbers from `min` (inclusive) to `max` (exclusive).
 */
const range = (min, max, acc = []) => {
  if (max < min) throw new Error('not supported!')
  if (min >= max) return acc
  return range(min + 1, max, acc.concat(min))
}

/**
 * Very minimal Unit-testing framework
 */
const assert = require('assert') // Node.js standard module
const tests = []
const test = (name, fn) => tests.push({ name, fn })
const run = () =>
  tests.forEach((t) => {
    try {
      t.fn()
      console.log(`\n✅ PASSED: ${t.name}`)
    } catch (e) {
      console.log(`\n❌ FAILED: ${t.name}`)
      console.error(e.message)
    }
  })

/**
 * Unit tests
 */
test('equal min-max works inclusive-exclusive', () => {
  assert.deepEqual(range(0, 0), [])
})
test('max is handled exclusively', () => {
  assert.deepEqual(range(0, 1), [0])
  assert.deepEqual(range(0, 2), [0, 1])
})
test('handles starting at higher numbers', () => {
  assert.deepEqual(range(5, 9), [5, 6, 7, 8])
})
test('supports negative numbers', () => {
  assert.deepEqual(range(-5, -3), [-5, -4])
  assert.deepEqual(range(-5, 3), [-5, -4, -3, -2, -1, 0, 1, 2])
})
test('does not support decreasing numbers', () => {
  assert.throws(() => range(8, 3))
})

run()