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Maria M.
Maria M.

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πŸ“š Writing Testable Code in React

In frontend development, writing testable code is crucial for maintaining the quality and maintainability of our applications. Here’s a simple and effective guide to ensure your React components are easy to test.

🧩 Break Down Components and Keep Them Simple

Divide your application into small, focused components, each with a single responsibility.

const Button = ({ label, onClick }) => (
  <button onClick={onClick}>{label}</button>
);
export default Button;
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🧠 Avoid Complex Logic in Components

Keep complex logic out of components, in functions that can be tested separately.

const calculateTotal = (items) => {
  return items.reduce((total, item) => total + item.price, 0);
};

const Cart = ({ items }) => {
  const total = calculateTotal(items);
  return <div>Total: ${total}</div>;
};
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πŸ› οΈ Use Props to Inject Dependencies

Inject data and functions through props instead of using global dependencies.

const UserGreeting = ({ user, logout }) => (
  <div>
    <p>Hello, {user.name}!</p>
    <button onClick={logout}>Logout</button>
  </div>
);
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βœ… Write Unit and Integration Tests

Unit Tests for individual functions:

import { calculateTotal } from './path/to/your/function';

test('calculates total correctly', () => {
  const items = [{ price: 10 }, { price: 20 }];
  expect(calculateTotal(items)).toBe(30);
});
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Integration Tests for components:

import React from 'react';
import { render, screen } from '@testing-library/react';
import Cart from './Cart';

test('renders total correctly', () => {
  const items = [{ price: 10 }, { price: 20 }];
  render(<Cart items={items} />);
  expect(screen.getByText('Total: $30')).toBeInTheDocument();
});
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🎭 Use Mocks and Spies

Use mocks to simulate dependencies and spies to verify interactions.

import React from 'react';
import { render, screen } from '@testing-library/react';
import UserGreeting from './UserGreeting';

test('renders user greeting', () => {
  const mockUser = { name: 'John' };
  const mockLogout = jest.fn();
  render(<UserGreeting user={mockUser} logout={mockLogout} />);

  expect(screen.getByText('Hello, John!')).toBeInTheDocument();
  screen.getByText('Logout').click();
  expect(mockLogout).toHaveBeenCalled();
});
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πŸ”§ Recommended Tools

  • React Testing Library: Facilitates integration tests and simulates user interactions. Documentation
  • Jest: Recommended testing framework for React, ideal for unit tests and mocks. Documentation

🌟 Best Practices

  1. ✏️ Write Tests First: Adopt TDD to ensure your code is testable from the start.
  2. 🧼 Keep Components Pure: Avoid global dependencies and shared states.
  3. πŸ“ Document Tests: Ensure tests are well-documented to facilitate maintenance.

🎯 Summary

  • 🧩 Simple Components: Facilitate unit testing.
  • 🧠 Separate Logic: Isolate complexity in functions.
  • πŸ› οΈ Props for Dependencies: Enhance testability.
  • βœ… Unit and Integration Tests: Ensure complete coverage.
  • 🎭 Mocks and Spies: Simulate dependencies and verify interactions.

By following these principles and practices, you will write testable React code, maintaining the high quality of your applications.

πŸ“š Additional Resources

Apply these concepts in your next project and see how your code quality and maintainability improve. Happy coding! πŸš€

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