JavaScript Unit Test

Section 01

Types of tests:

• Unit Testing
  • If all building blocks works, the overall app works
• Integration Testing
  • Even if all units work standalone, the combination could fail
• End-to-End (E2E) Testing
  • Real ursers use your app and its features, not individual units

All of those type of tests should be combined when is doing tests.

The Testing Pyramid

• E2E Tests
• Integration Tests
• Unit Tests

Test-Driven Development (TDD)

A framework / philosophy for writing tests

1. Write a failing test first
2. Implement the code to make the test succeed
3. Refactor

Course steps

1. Getting started
2. Project Setup & Required Tools
3. Testing Fundamentals
4. Writing Good Tests
5. Advanced Testing Concepts
6. Mocks & Spies
7. Diving Deeper into Mocks & Spies
8. Tests & The DOM

Section 02

• Adjusting the Development Environment
  • Required Tools
  • An Example Setup
  • Alternatives

Automated Tests

• Test Runner
  • Runs your tests (i.e, the testing code)
  • Automatically detects testing code
  • Displays results
  • e.g., Jest, Karma
  • Expect results
• Assertion Library
  • Used to define expected outcomes
  • Checks whether expectations are met
  • Supports all kinds of expectations and modes (sync / async)
  • e.g., Jest, Chai

ECMAScript on Jest have a experimental support an alternative is Vitest

Section 03

The Basics

• Understanding Unit Testing Fundamentals
  • Creating Unit Tests
  • AAA - Arrange, Act, Assert
  • What To Test & Organizing Tests

How it works? Write the test function that the first argument is the description of what the test will do and the second one is the test itself.

Example:

import {it} from 'vitest'

it('the description', () => {})

The AAA Pattern - Arrange, Act, Assert

• Arrange: Define the testing environment and values
• Act: Run the actual code / function that should be tested
• Assert: Evaluate the produced value / result and compare it to the expected value / result

Keep Your Tests Simple!

Writing good tests is an iterative process

Note Technically, expect() does not return true or false. Instead, it throws an error, if the expection is not met. The test runner treats thrown errors as failed tests and tests that do not throw as passed.

It's ok to write more than one test with the same result, but it can be arranged in the same test to avoid repetition.

Section 04

Important: ONLY TEST YOUR CODE

How to write good tests

Follow Arrange-Act-Assert

• Only test one thing
• Focus on essence of a test when arranging
• Keep your number of assertions ("expects") low

Splitting functions for easier testing and better code.

Section 05

Integration Tests