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Simple introduction to unit test

Unit test 🧪

In computer programming, unit testing is a software testing method by which individual units of source code—sets of one or more computer program modules together with associated control data, usage procedures, and operating procedures—are tested to determine whether they are fit for use. (Wikipédia)

Benefit of Unit testing (UT)

  • Verify if a change (code) has created a bug or changed the behavior somewhere in the application
  • 🐛 Find the root of the bug easily
  • 📈 Improve software quality
  • 🙌 Your teammates will thank you

A simple good test:

Has this specifications:

1. Clean code

Test code remains "code" so we should also try to respect good practices (ex: DRY, KISS, Single Responsibility... ), linters, recent langage...

👉 In order to keep the reliability, understanding and maintainability. for your team.

2. Independence

"Unit". Should not depend on the other tests. For example: tests should be able to be run in any order.

Avoid as much as possible the dependance of other systems/code of your software/app like instantiations for example, you can use mock data or stubs to avoid this.

3. Test the necessary

I don't know if everyone will be agree with this, but ...

We don't need to test all functions/routes/libs(...) or at least not right now... 😌

  • Prioritize the code that you change most often.

We can be discouraged by the HUGE work to cover all our app... We can start step by step and cover just 1 small part of our app. (let me know your opinion 🙏 )

4. Understanding 📖

Naming. We should understand the test when see the test name.

This is good pattern that works for me:

[unit name] ... [should] ... [when] ... context

The name should be composed by the description, then the pattern 'should' (result we expect) and optionally 'when' that describes the scenario or context.

Tips : If the test becomes bigger, divide it into small pieces.

➕ Bonus: Phases/Structure

Must know is AAA (arrange, act, assert).

  • Arrange: prepare -> mocks, before method (), parameters(context) for our function

  • Act: basically call the function/unit work that we want to test

  • Assert: define the result that you expect

Tips : Avoid many 'expect' for only one test, to keep Single Responsibility.


I will use AVA library for tests

A basic & Simple Test preFlight request

test('isPreFlightRequest should be true when request method is OPTIONS', (t) => {
  const mockRequest = {
    method: 'OPTIONS',

  // ACT
  const ispreFlightRequest = cors.isPreFlightRequest(mockRequest);

  //ASSERT, true, 'ispreFlightRequest should return true');



You can also read this

Thank for reading 🙇‍♂️

Top comments (2)

shannannon profile image

Thanks for sharing such a clean and easy to understand tutorial!

bladesensei profile image

Thank Shannon !