Basic example of using Jest for testing exported node module

Jest-TDD-ExportedNodeModule-Example.js

/*
  
  Filename ./myModule.js

*/

let a = (obj)=>{
    return obj.x * obj.y
}
let b = (obj)=>{
    return obj.x / obj.y
}
let c = (obj)=>{
    return obj.x + obj.y
}

module.exports = {
    a,
    b,
    c
}

/*
  
  Install Jest as dev dependency (npm install --save-dev jest)
  Inside package.json set npm scripts.test to "jest"
  Run from command line: npm test
  
  Filename: ./tests/myModule.test.js
  
*/

let myModule = require('../myModule')

it('should multiply two values', () => {
    expect(myModule.a({
        x: 10,
        y: 10
    })).toBe(100) 
})

it('should divide two values', () => {
    expect(myModule.b({
        x: 10,
        y: 10
    })).toBe(1) 
})

it('should add two values', () => {
    expect(myModule.c({
        x: 10,
        y: 10
    })).toBe(20) 
})