Node has a build in testing with a library called 'assert'. In my previous project, I started to do some Test-Driven Development (TDD) approach with raw node.js. And then, I came accross with 'assert' that is build in with Node.js and it turns out that the API is easy to get started.

What Will I Learn?

• Basic Test-Driven Development (TDD) in Node.js
• Using of assert library which is build in library of Node.js

Requirements

• Node.js
• Node.js REPL

Difficulty

Intermediate

Tutorial Contents

'assert' is a light testing library that is build into Node.js. For this tutorial I am using Node v8.9.2 .

One of the thing I learn from Test-Driven Development is that you should always make sure your test code are always bug-free. So, always check few times for the test code.

In REPL mode

Run node in terminal, and use assert to see what functions are available.

These are the exist function in assert

The reason running on REPL first is to try out how the library works.

The reason behind that you can just type assert without using something like var assert = require('assert') is because node.js has included assert into the REPL library.

OK

When assert.ok(value) is used, assert will make sure that the value in it is always true.

$ assert.ok(1);
undefined
$ assert.ok(false);
AssertionError [ERR_ASSERTION]: false == true
$ assert.ok();
AssertionError [ERR_ASSERTION]: undefined == true

Equal, Not Equal

Equal

When assert.equal(LHS, RHS) is used, assert will compare Left Hand Side value to the Right Hand Side value, which is very useful to test for behaviour.

$ assert.equal(7,7);
undefined
$ assert.equal(7,8);
AssertionError [ERR_ASSERTION]: 7 == 8

Not Equal

When assert.notEqual is used, assert will do exactly the opposite of the Equal

$ assert.notEqual(1,2);
undefined
$ assert.notEqual(1,1);
AssertionError [ERR_ASSERTION]: 1 != 1

ifError

This function is used to throw if there is an error.

function throwError() {
  throw('error');
}
assert.ifError(throwError());

Used it in js file

Sample Project 1: Testing Regex

Since REPL mode to try out is done, I would like to share a bit to change my existing testing code from raw node.js to assert library.

The testing code is used to test the REGEX for the project which the source code is on GitHub.

You do not need to really understand the variable name, basically I want to make sure the REGEX does what I expect it to do.

The old code

function regexTest() {
  console.log('==========REGEX TEST START==========');
  // Image test
  let resultFile = imageParser(sourceFile);
  console.log('imagePaser test:');
  console.log(resultFile === imgFile);
  // Link test
  console.log('linkPaser test:');
  console.log(linkParser(resultFile) === linkFile);
  console.log('========== REGEX TEST END ==========');
}

The way I test is using console.log() in node.js, which is suitable for simple thing as this.

By using assert library, the source code can be like this.

Using assert library

const assert = require('assert');
function regexTest() {
  // Image Test
  assert.equal(imageParser(sourceFile), imgFile);
  // Link Test
  assert.equal(linkParser(resultFile), linkFile)
}

Sample Project 2: Testing with reading a file

In this second sample, we will make use of 'fs' library which is build in with Node.js.

const fs = require("fs");
const assert = require("assert");
function fileExist(cb) {
  fs.readFile("test.txt", "utf8", (err, src) => {
    if (err) {
      return cb(err);
    } else {
      return cb(null, src);
    }
  });
}
fileExist((err, src) => {
  assert.ifError(err);
  console.log(src);
});

What this file do is that it read the file called test.txt, and if it exist, it will return err to be null and src to be what is in the file. On the other hand, if the file does not exist, it will return err with the callback.

So, if error exist, we are going to use assert.ifError(err) to throw out the error if the file does not exist.

Then, create a file called test.txt to make the test success.

If you not sure wether the code exitted successfully, you can always run echo $? to see what exit code is it. In node.js, 0 means it exit successfully.

Final thoughts

'assert' library is suitable for small scale testing. It is not suitable for large project because 'assert' library will stop execution when they met an error, and the test also will take longer time if there is many test cases.

Therefore, if sometimes when you need some extra feature like using HTTP method, it would be wise to use other testing framework like Tape, Mocha and Jasmine.

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Posted on Utopian.io - Rewarding Open Source Contributors

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