Below is a basic guide on setting up E2E testing with NextJS, Resend, and Playwright.

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1. Create an endpoint.

For simplicity, we’ll create a GET endpoint that sends an email to the testing account, delivered@resend.dev on fetch.

app/api/send/route.ts
import { Resend } from 'resend';
const resend = new Resend(process.env.RESEND_API_KEY);

export async function GET() {
  try {
    const { data, error } = await resend.emails.send({
      from: 'Acme <onboarding@resend.dev>',
      to: ['delivered@resend.dev'],
      subject: 'Hello world',
      html: '<h1>Hello world</h1>',
    });

    if (error) {
      return Response.json({ error }, { status: 500 });
    }

    return Response.json({ data });
  } catch (error) {
    return Response.json({ error }, { status: 500 });
  }
}

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2. Write the test spec file.

Create a test spec file at e2e/app.spec.ts. You can test in two ways:

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Option 1: Call the Resend API

Calling the Resend API tests the entire API flow, including Resend’s API responses, but counts towards your account’s sending quota.

e2e/app.spec.ts
import { test, expect } from '@playwright/test';

test('does not mock the response and calls the Resend API', async ({
  page,
}) => {
  // Go to the page
  await page.goto('http://localhost:3000/api/send');

  // Assert that the response is visible
  await expect(page.getByText('id')).toBeVisible();
});

​
Option 2: Mock a response

Mocking the response lets you test your app’s flow without calling the Resend API and impacting your account’s sending quota.

e2e/app.spec.ts
import { test, expect } from '@playwright/test';

test("mocks the response and doesn't call the Resend API", async ({ page }) => {
  // Sample response from Resend
  const body = JSON.stringify({
    data: {
      id: '621f3ecf-f4d2-453a-9f82-21332409b4d2',
    },
  });

  // Mock the api call before navigating
  await page.route('*/**/api/send', async (route) => {
    await route.fulfill({
      body,
      contentType: 'application/json',
      status: 200,
    });
  });

  // Go to the page
  await page.goto('http://localhost:3000/api/send');

  // Assert that the response is visible
  await expect(page.getByText(body)).toBeVisible();
});

However you test, it’s important to test using a test email address (e.g., delivered@resend.dev) so your tests don’t impact your deliverability. Resend’s test accounts run through the entire API flow without harming your reputation.

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3. Create a Playwright config file.

Write your config file, paying special attention to a few properties:

  • testDir: the directory containing your test files
  • outputDir: the directory to store test results
  • webServer: provide instructions for Playwright to run your app before starting the tests
  • projects: an array of the browsers you want to test
playwright.config.ts
import { defineConfig, devices } from '@playwright/test';
import path from 'path';

const baseURL = 'http://localhost:3000';

export default defineConfig({
  timeout: 30 * 1000,
  testDir: path.join(__dirname, 'e2e'),
  retries: 2,
  outputDir: 'test-results/',
  webServer: {
    command: 'npm run dev',
    url: baseURL,
    timeout: 120 * 1000,
    reuseExistingServer: !process.env.CI,
  },

  use: {
    baseURL,
    // Retry a test if its failing with enabled tracing. This allows you to analyze the DOM, console logs, network traffic etc.
    trace: 'retry-with-trace',
  },

  projects: [
    // Test against desktop browsers.
    {
      name: 'Desktop Chrome',
      use: {
        ...devices['Desktop Chrome'],
      },
    },
    {
      name: 'Desktop Firefox',
      use: {
        ...devices['Desktop Firefox'],
      },
    },
    {
      name: 'Desktop Safari',
      use: {
        ...devices['Desktop Safari'],
      },
    },
    // Test against mobile viewports.
    {
      name: 'Mobile Chrome',
      use: {
        ...devices['Pixel 5'],
      },
    },
    {
      name: 'Mobile Safari',
      use: devices['iPhone 12'],
    },
  ],
});

See the Playwright docs for more help.

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4. Run the test.

You can run the test by installing Playwright and running the tests.

npx playwright install
npx playwright test

Playwright will run the tests in the browsers of your choice and show you the results.

Example repo

See the full source code.

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