├── calculator.js
├── package.json
├── calculator-test.js
├── README.md
└── test.js


/calculator.js:
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1 | const add = (a, b) => a + b
2 | 
3 | const subtract = (a, b) => a - b
4 | 
5 | module.exports = {
6 |         add,
7 |         subtract
8 | }


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/package.json:
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 1 | {
 2 |   "name": "nodejs-test-without-library",
 3 |   "version": "1.0.0",
 4 |   "description": "",
 5 |   "main": "index.js",
 6 |   "scripts": {
 7 |     "test": "node test.js ./*-test.js"
 8 |   },
 9 |   "author": "",
10 |   "license": "ISC"
11 | }


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/calculator-test.js:
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 1 | const assert = require('assert')
 2 | const { add, subtract } = require('./calculator')
 3 | 
 4 | test('should add two numbers', () => {
 5 |         assert.equal(add(1, 2), 3)
 6 | })
 7 | 
 8 | test('should subtract two numbers', () => {
 9 |         assert.equal(subtract(3, 2), 1)
10 | })


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/README.md:
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 1 | # Node.js Testing Without Libraries
 2 | 
 3 | This is a sample project demonstrating how to write, and run tests for Node.js without using an external library.
 4 | 
 5 | For the complete explanation, you can see my [blog post](https://www.sohamkamani.com/blog/javascript/making-a-node-js-test-runner/).
 6 | 
 7 | To run the tests, clone this repo and run:
 8 | 
 9 | ```
10 | npm test
11 | ```
12 | 
13 | You can change one of the tests in `calculator-test.js` and run `npm test` again to see the test failure message.


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/test.js:
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 1 | // `tests` is a singleton variable that will contain all our tests
 2 | let tests = []
 3 | 
 4 | 
 5 | // The test function accepts a name and a function
 6 | function test(name, fn) {
 7 | 	// it pushes the name and function as an object to
 8 | 	// the `tests` array
 9 | 	tests.push({ name, fn })
10 | }
11 | 
12 | function run() {
13 | 	// `run` runs all the tests in the `tests` array
14 | 	tests.forEach(t => {
15 | 		// For each test, we try to execute the
16 | 		// provided function. 
17 | 		try {
18 | 			t.fn()
19 | 			// If there is no exception
20 | 			// that means it ran correctly
21 | 			console.log('✅', t.name)
22 | 		} catch (e) {
23 | 			// Exceptions, if any, are caught
24 | 			// and the test is considered failed
25 | 			console.log('❌', t.name)
26 | 			// log the stack of the error
27 | 			console.log(e.stack)
28 | 		}
29 | 	})
30 | }
31 | 
32 | // Get the list of files from the command line
33 | // arguments
34 | const files = process.argv.slice(2)
35 | 
36 | // expose the test function as a global variable
37 | global.test = test
38 | 
39 | // Load each file using `require`
40 | files.forEach(file => {
41 | 	// Once a file is loaded, it's tests are
42 | 	// added to the `tests` singleton variable
43 | 	require(file)
44 | })
45 | 
46 | // Now that all the tests from all the files are
47 | // added, run them one after the other
48 | run()


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