Mastering Testing and Error Handling in Next.js

Why Testing and Error Handling Matter

Testing ensures that your code is efficient and saves you hours of debugging time. Error handling, on the other hand, makes your application more user-friendly by redirecting users to custom error pages when errors occur. Next.js provides APIs for proper error handling, taking your application to the next level.

Getting Started with Testing and Error Handling in Next.js

To get the most out of this article, you’ll need some basic knowledge of JavaScript, React, and Next.js, as well as experience with testing JavaScript libraries and frameworks.

Testing Options for Next.js Applications

Next.js recommends three testing libraries: Cypress, Playwright, and Jest and React Testing Library. In this article, we’ll focus on testing Next.js applications using Cypress.

Testing Next.js Elements with Cypress

Cypress is an end-to-end, JavaScript-based testing framework that allows you to run tests on your Next.js application. To get started, create a basic Next.js application, install Cypress, and set up a test script in your package.json file:

{
  "scripts": {
    "test": "cypress run"
  },
  "devDependencies": {
    "cypress": "^9.3.1"
  }
}

Then, create a test file, for example, cypress/integration/example.spec.js, and write your tests using Cypress commands:

describe('Example page', () => {
  it('should render the page', () => {
    cy.visit('/')
    cy.get('h1').should('have.text', 'Welcome to my Next.js app')
  })
})

Testing API Routes in Next.js

When working with larger applications, you may need to test routes and endpoints. Cypress can help you achieve this. Create an API route in your Next.js application, for example, pages/api/hello.js:

import { NextApiRequest, NextApiResponse } from 'next';

export default async function handler(req: NextApiRequest, res: NextApiResponse) {
  res.status(200).json({ message: 'Hello from API route' });
}

Then, define tests for it using Cypress:

describe('API route', () => {
  it('should return a JSON response', () => {
    cy.request('GET', '/api/hello').then(response => {
      expect(response.status).to.eq(200)
      expect(response.body).to.have.property('message', 'Hello from API route')
    })
  })
})

Error Handling in Next.js

There are three types of errors in Next.js: errors in development, client errors, and server errors. Errors in development occur during development and are thrown as an error overlay or modal. Client errors are handled using the React Error Boundary API, while server errors occur in Next.js data fetching methods and can be handled using try…catch blocks.

Rendering Custom Error Pages in Next.js

Next.js provides an inbuilt Error component that handles both server-side and client-side 500 errors. To customize this component, create a pages/_error.js file and import it into your application:

import Head from 'next/head';

function ErrorPage() {
  return (

  );
}

export default ErrorPage;

By mastering testing and error handling in Next.js, you can build more efficient, user-friendly applications. With tools like Cypress, you can take your development skills to the next level and create exceptional digital experiences.