NodeJs testing example, 'requiring' chai, run with terminal command: mocha <location of file> (e.g. mocha test.js)

test.js

'use strict';

const expect = require( 'chai' ).expect;

// testing example function f (you normally "require" the file you want to test)
function f( x ) {

    return( x + x + x + x );
}

// the "describe" function works when you run this file with mocha
// "describe" gives what you're testing a description
describe( 'testing function f', function() {

    // "its" are sections within your "describe" that contain the specific tests you want to do
    it( 'with x = 5', function() {

        let test_x = 5;

        let expected_value_of_f = 4 * test_x;

        expect( f( test_x ) ).to.equal( expected_value_of_f );
    });

    it( 'with x = 0', function() {

        let test_x = 0;
        
        let expected_value_of_f = 0;

        expect( f( test_x ) ).to.equal( expected_value_of_f );
    });
});

/*
    Links:
    
    Chai ----> https://github.com/chaijs/chai-http
    
    Mocha ---> https://mochajs.org/
*/