Testing ES6 module in mocha

to test ES6 modules in the testing framework mocha after importing them, we need to add some settings.

1. Installing dependencies

install mocha as devDependencies

console
$ npm install mocha --savedev

install @babel/XXX as devDependency

console
$ npm install \
  @babel/cli \
  @babel/core \
  @babel/preset-env \
  @babel/register \
  --save-dev

package.json should be like

package.json
{
  "scripts": { ... }
  "devDependencies": {
    "@babel/cli": "^7.15.7",
    "@babel/core": "^7.15.5",
    "@babel/preset-env": "^7.15.6",
    "@babel/register": "^7.15.3",
    ...
    "mocha": "^9.1.2",
    ...
  },
  ...
}

• mocha 9.x.x
• babel 7.x.x

2. Creating babel configuration file

Create a file .babelrc in [ROOT-DIR]

TXT
[ROOT-DIR]
 +- src
 +- test
 +- package.json
 +- .babelrc (+)

input the content

.babelrc
{
  "presets": ["@babel/preset-env"]
}

3. Sample files

We will create two files to validate current configuration

• src/calc.js - source file under test
• test/calc.spec.js - test file

TXT
[ROOT-DIR]
 +- src
     +- calc.js (+)
 +- test
     +- calc.spec.js (+)
 +- package.json
 +- .babelrc

input the content

src/calc.js
const add = (a, b) => a + b
const mul = (a, b) => a - b

export default {
  add,
  mul
}

test/calc.spec.js
import assert from 'assert'
import calc from '../src/calc'

describe('testing calculator', () => {
  it('should be seven', () => {
    const seven = calc.add(3, 4)
    assert.equal(7, seven)
  })
})

4. Test Command

Now, create test command in package.json to be executed with npm run ...

package.json
{
  "scripts" {
    "build": ... ,
    "start": ... ,
    "test": mocha --require @babel/register (+)
  }
}

5. Test run

run in terminal

console
$ npm run test

• npm run test - will execute 'test' of "scripts" in package.json

result

test_result
$ npm run test

  testing calculator
    ✔ should be seven


  1 passing (7ms)