nodejs_jest.md

NodeJS - Bootstrapping Jest Test Suite

Here's instructions on installing Jest and bootstrapping for ES6 module compilation for Node.

Note: This guide assumes you have NodeJS installed.

1. Create a new project folder for the code:

   (Assuming project name is new_kata)

   mkdir new_kata
   cd new_kata

2. In the new project folder, create package.json

   yarn init

   or

   npm init

3. Add packages

   yarn add --dev jest @babel/core @babel/preset-env

   or

   npm install --save-dev jest @babel/core @babel/preset-env

4. Add test running script in package.json

   "scripts": {
     "test": "jest",
     "test:watch": "jest --watch"
   }

5. Create a .babelrc with these content for a smart preset babel configuration

   {
   	"presets": [
   		["@babel/preset-env",
   			{
   				"targets": {
   					"node": "10"
   				}
   			}
   		]
   	]
   }

6. Create a code (sum.js) file

   const sum = (a, b) => a + b
   export default sum

7. Create a test (sum.test.js) file

   import sum from './sum'
   
   test('adds 1 + 2 to equal 3', () => {
     expect(sum(1, 2)).toBe(3);
   });

8. You can run the test:

   yarn test

   or

   npm test

   You should see this:

   yarn run v1.9.4
   $ jest
    PASS  ./sum.test.js
     ✓ adds 1 + 2 to equal 3 (3ms)
   
   Test Suites: 1 passed, 1 total
   Tests:       1 passed, 1 total
   Snapshots:   0 total
   Time:        1.286s
   Ran all test suites.
   ✨  Done in 2.39s.

9. Read up more about the types of test matchers available in Jest: https://jestjs.io/docs/en/using-matchers