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Testing

Testing in JavaScript helps ensure your code behaves as expected. It involves writing small code snippets called tests that automatically verify your functions, logic, and components.

Illustration of Testing
Illustration of Testing

💡 Why Test?

Detect bugs early, improve code reliability, and facilitate safe refactoring.

Types of Testing

  • Unit Testing: Test individual functions or modules in isolation.
  • Integration Testing: Test how different parts work together.
  • End-to-End Testing: Simulate real user scenarios in the full application.

Basic Testing with Assertions

At its core, testing asserts that expected outcomes match actual outcomes. You can use simple if statements or testing libraries.

📌 Deep Dive: Simple Assertion

JAVASCRIPT
function add(a, b) {
  return a + b;
}

// Test
if (add(2, 3) === 5) {
  console.log('Test passed');
} else {
  console.error('Test failed');
}
Output
Test passed

Using Jest for Testing

Jest is a popular JavaScript testing framework that simplifies writing and running tests.

📌 Deep Dive: Jest Test Example

JAVASCRIPT
const add = (a, b) => a + b;

test('adds 2 + 3 to equal 5', () => {
  expect(add(2, 3)).toBe(5);
});
Output
PASS ./add.test.js
✓ adds 2 + 3 to equal 5 (5 ms)

Common Testing Methods

Jest Expect Matchers
MatcherPurpose
toBe(value)Exact equality (===)
toEqual(value)Deep equality (objects, arrays)
toBeTruthy()Value is truthy
toThrow()Function throws an error

⚠️ Important

Tests should be isolated, fast, and repeatable. Avoid side effects and dependencies on external resources like databases or APIs in unit tests.

Testing Best Practices

  • Write tests for both expected and edge cases.
  • Name tests clearly to describe the behavior tested.
  • Run tests frequently during development.
  • Keep tests small and focused on one behavior.

💡 Tip

Use continuous integration (CI) tools to run tests automatically on code changes.

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