Testing ES6 module in mocha

테스트 프레임워크 mocha에서 ES6 모듈 import 후 테스트를 하려면 몇가지 설정을 추가해야 합니다.

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)