Jest is a JavaScript testing framework that is focused on simplicity. It allows you to write tests with an accessible, familiar, and feature-rich API that gives you test results quickly.
- It helps to write a fast and safe test case, which runs parallel.
- it can generate code coverage by adding the flag --coverage
- it allows easy mocking of functions and APIs.
Installing 🔌 JEST
Using npm
npm install --save-dev jest
Using yarn
yarn add --dev jest
Writing Simple Test
create a node project using npm
npm init
Folder Structure 🗂
let's put some sample functions to test in index.js
function sum(a, b) {
console.log("adding values ", a, " ", b);
return a + b;
}
function diff(a, b) {
console.log("diff between values ", a, " ", b);
return a - b;
}
function mul(a, b) {
console.log("multiplying values ", a, " ", b);
return a * b;
}
function div(a, b) {
console.log("dividing values ", a, " ", b);
return a / b;
}
function mod(a, b) {
console.log("modulus values ", a, " ", b);
return a % b;
}
module.exports = {
sum: sum,
diff: diff,
mul: mul,
div: div,
mod: mod
};
now, we need to install jest and do the configuration in the package.json file.
Inside the scripts key, we define a jest test logic.
"scripts": {
"test": "jest"
},
Time to write some test, to ensure correct working of our functions. Inside index.test.js import our file.
const cal = require('../index');
writing test 💻 for the sum function
const cal = require('../index');
test('adds 1 + 2 to equal 3', () => {
expect(cal.sum(1, 2)).toBe(3);
expect(cal.sum(1, 2)).not.toBe(4);
expect(cal.sum(1, 2)).toBeGreaterThan(2);
expect(cal.sum(1, 2)).toBeLessThan(4);
expect(cal.sum(1, 2)).toBeCloseTo(3);
// Testing datatype
expect(typeof cal.sum(1, 2)).toBe("number");
});
Running the test from terminal
npm run test
we run our first test, everything works fine. but the value of a, b is hardcoded, we will use Math.floor(Math.random() * 11) function for generating a and b. For Repeating SetUp we will use the beforeEach hook, Which is used if we have some work we need to do repeatedly for many tests.
beforeEach(() => {
a = Math.floor(Math.random() * 100);
b = Math.floor(Math.random() * 100);
});
Complete Testing Code
const cal = require('../index');
let a;
let b;
beforeEach(() => {
a = Math.floor(Math.random() * 100);
b = Math.floor(Math.random() * 100);
});
test(" testing sum " + a + " " + b + " function ", () => {
expect(cal.sum(a, b)).toBe(a + b);
expect(cal.sum(a, b)).not.toBe(a + b + 1);
expect(cal.sum(a, b)).toBeGreaterThan(a + b - 1);
expect(cal.sum(a, b)).toBeLessThan(a + b + 1);
expect(cal.sum(a, b)).toBeCloseTo(a + b);
// Testing datatype
expect(typeof cal.sum(a, b)).toBe("number");
});
test(" testing diff " + a + " " + b + " function ", () => {
expect(cal.diff(a, b)).toBe(a - b);
expect(cal.diff(a, b)).not.toBe(a - b + 1);
expect(cal.diff(a, b)).toBeGreaterThan(a - b - 1);
expect(cal.diff(a, b)).toBeLessThan(a - b + 1);
expect(cal.diff(a, b)).toBeCloseTo(a - b);
// Testing datatype
expect(typeof cal.diff(a, b)).toBe("number");
});
test(" testing mul " + a + " " + b + " function ", () => {
expect(cal.mul(a, b)).toBe(a * b);
expect(cal.mul(a, b)).not.toBe(a * b + 1);
expect(cal.mul(a, b)).toBeGreaterThan(a * b - 1);
expect(cal.mul(a, b)).toBeLessThan(a * b + 1);
expect(cal.mul(a, b)).toBeCloseTo(a * b);
// Testing datatype
expect(typeof cal.mul(a, b)).toBe("number");
});
test(" testing div " + a + " " + b + " function ", () => {
expect(cal.div(a, b)).toBe(a / b);
expect(cal.div(a, b)).not.toBe(a / b + 1);
expect(cal.div(a, b)).toBeGreaterThan(a / b - 1);
expect(cal.div(a, b)).toBeLessThan(a / b + 1);
expect(cal.div(a, b)).toBeCloseTo(a / b);
// Testing datatype
expect(typeof cal.div(a, b)).toBe("number");
});
test(" testing mod " + a + " " + b + " function ", () => {
expect(cal.mod(a, b)).toBe(a % b);
expect(cal.mod(a, b)).not.toBe(a % b + 1);
expect(cal.mod(a, b)).toBeGreaterThan(a % b - 1);
expect(cal.mod(a, b)).toBeLessThan(a % b + 1);
expect(cal.mod(a, b)).toBeCloseTo(a % b);
// Testing datatype
expect(typeof cal.mod(a, b)).toBe("number");
});
Top comments (4)
Good introduction really wish more developers would learn testing at the start so that its easier down the line.
Thanks ☺️
Hi, congrats. Jest is a really good test framework but I'd like to suggest starting using Node Tap. Different Jest which changes global objects, Node Tap is simple and lightweight.
Thanks, sure will try node tap