Best Practices for API Testing with Playwright in a Software Development Company

Modern software development hinges on the seamless interaction between various components and external services. Application Programming Interfaces (APIs) serve as the communication layer facilitating this exchange. While their presence may be subtle, their role is undeniable.

Therefore, a software development company must focus on robust API testing. Now the question is, which one is appropriate for API testing?

There are many names in the software development industry, but Playwrite excels in this game. So, is Playwright good for API testing? The answer is "yes."

Keep reading the blog to discover the best practices for Playwright API testing.

Why is API testing essential for a software development company?

Robust API testing emerges as an essential practice for a software development company in the US for several reasons:

Functional validation

APIs reveal the capabilities that different components of an application or external systems depend on. Comprehensive testing of APIs guarantees these capabilities work as expected, following set standards and data agreements. Instruments such as Postman or Curl can issue test requests and check the results against the expected formats and structures.

Early issue identification

Adopting a left-to-right approach in software development, which focuses on identifying problems early, is crucial. API testing allows developers to spot and fix issues within the API layer before affecting other systems. This strategy prevents the need for expensive bug fixes later in the development process.

Better reliability and efficiency

APIs are the foundation of data sharing. API testing aids in pinpointing areas that slow down performance and ensures that responses are provided within reasonable times. Tools for load testing can replicate large numbers of requests to evaluate how APIs handle increased traffic and remain stable.

Improved security

Cyber threats often target APIs. API testing includes security aspects, such as ensuring that authentication processes work properly and access is granted as planned. Tools for fuzzing can be used to test APIs for possible weaknesses.

Best API testing practices with Playwright in software development

Below are the best practices to empower a software development company to conduct effective Playwright tests for APIs:

Define the end-to-end test coverage goals

Before creating tests, it's essential to have a well-defined plan for the main features that need to be tested. Not every process requires testing from start to finish (E2E). A practical strategy focuses on the essential features necessary for running the business smoothly.

For a RESTful API, this could cover the following:

• Authenticating users and controlling their access
• Carrying out CRUD (Create, Read, Update, Delete) operations on crucial data structures
• Connecting with outside services

Analyzing user behavior using tools that show the most used API endpoints can help developers decide which parts of the code need testing most. These tools can also find less common but still important functions, like resetting passwords. Even though these processes are rarely used, their problems can upset users. Adding them to the test plan makes finding and fixing issues quicker.

After deciding on the essential tasks, developers can create a focused and thorough test plan that meets the testing requirements.

Embrace stable selectors to locate elements

Playwright offers built-in assertion methods to validate data returned by API responses. These assertions use selectors to target specific elements within the JSON response object. Utilizing stable selectors is paramount
for maintaining reliable and non-flaky tests.

Here's an example utilizing Playwright's test and expect methods to assert the presence of a specific key within a JSON response:

test('GET /users/:id returns user details', async ({ request }) => {
  const response = await request.get('/users/123');
  const data = await response.json();
  expect(data).toHaveProperty('name');
});

In this example, the toHaveProperty assertion method leverages a property name as a selector to target the desired element within the response object. This approach offers several advantages:
Resilience against schema changes: Minor schema modifications, such as property renames, won't necessarily break tests as long as the overall data structure remains similar.
Maintainability: Tests remain clear and focused on the validated data, increasing maintainability for a software development company.
Flexibility: Selectors can be chained to target nested elements within the response object.

Keep the tests focused and isolated

Playwright fosters isolated test environments. Each test executes with its own in-memory representation of the API state. This isolation ensures that tests are unaffected by the outcomes or side effects of other tests, promoting independent and reliable test results.

To benefit from this architecture, developers should keep their tests streamlined and focused, ensuring they precisely reflect the workflow under examination. For instance, consider testing a user login functionality:

test('POST /login authenticates a valid user', async ({ request }) => {
  const loginData = {
    username: 'johndoe',
    password: 'secret123',
  };
  const response = await request.post('/login', loginData);
  expect(response.status()).toBe(200);
  expect(await response.json()).toHaveProperty('token');
});

This test is focused solely on the login functionality. It sends a POST request with login credentials and asserts a successful response with a 200 status code and the presence of an access token within the response body.

Bundling additional functionalities, such as retrieving user details after successful login, compromises the ability to test each operation in isolation and could lead to cascading failures across the test suite.

Craft assertions from an end-user perspective

Meaningful assertions mimic user interactions and expectations when interacting with the API. They go beyond simply verifying the presence of elements within the response. Instead, they ensure the API's behavior aligns with what users would expect.

This includes verifying:

• The presence or absence of specific data fields
• Data types and formatting of returned values
• Expected error messages for invalid requests
• Status codes indicating successful or failed operations For example, when a user tries to set up a new account using a current email address, a meaningful assertion could check that the response contains an error message indicating the email address conflict:

test('POST /users creates a new user', async ({ request }) => {
  const userData = {
    email: '[e-mail]',
    password: 'securepassword',
  };
  const response = await request.post('/users', userData);
  expect(response.status()).toBe(400);
  expect(await response.json()).toHaveProperty('error');

Utilize descriptive tests and step titles for clarity

Developers of a custom software development company in the USA often encounter a failing test after hours of refactoring. The test output resembles the following:

error: Timed out waiting for expected condition

Deciphering the issue from such output becomes a daunting task, requiring examination of test scripts to identify the root cause. Descriptive test and step titles offer a clear advantage:

test.describe('User Authentication', () => {
  test('POST /login authenticates a valid user', async ({ request }) => {
    // Test steps and assertions
  });

  test('POST /login returns an error for invalid credentials', async ({ request }) => {
    // Test steps and assertions
  });
});

These titles not only indicate the functionalities being tested but also the specific actions and expected outcomes. Playwright supports structuring tests with clear steps, each with its own descriptive title. This approach streamlines troubleshooting and prevents tests from becoming overloaded with unnecessary checks.

Test across all relevant browsers

Modern web applications often interact with APIs through browser-based JavaScript code. Playwright simplifies cross-browser testing, ensuring that API integrations function flawlessly across various user environments. Projects can be established within the Playwright configuration file, specifying the browsers or devices targeted for testing.

const { defineConfig } = require('@playwright/test');

module.exports = defineConfig({
  projects: [
    {
      name: 'Chromium',
      use: { ...require('playwright/devices').chromium },
    },
    {
      name: 'Firefox',
      use: { ...require('playwright/devices').firefox },
    },
    {
      name: 'Webkit',
      use: { ...require('playwright/devices').webkit },
    },
  ],
});

The provided code snippet showcases configurations for Chromium, Firefox, and WebKit browsers. Playwright also supports testing against branded browsers like Chrome, Safari, and Edge. It also emulates mobile and tablet viewports for comprehensive testing in a software development consulting company.

Automate and monitor your tests

Running tests solely on a local development environment is insufficient for a robust development cycle. Integration with CI/CD pipelines is crucial for monitoring tests alongside builds. Ideally, tests should execute on every code commit and pull request. Playwright provides sample configurations for popular CI providers like GitHub Actions, Azure Pipelines, and CircleCI, facilitating seamless integration.

As the test suite grows, execution time becomes a consideration that can impact development velocity. Playwright offers parallel test execution by default, leveraging available CPU cores for faster testing. Further optimization can be achieved through test sharding, which involves splitting the test suite into multiple parts that can be executed concurrently on separate machines.

npx playwright test --shard=1/2
npx playwright test --shard=2/2

These commands illustrate sharding a test suite into two parts, enabling parallel execution on two machines. The generated reports can then be merged for consolidated test results. Many CI platforms support parallel job execution, further accelerating the testing process.

Don't test third-party integrations directly

Web applications frequently rely on third-party APIs for functionalities like payments, social logins, or data analytics. Integrating these directly into E2E tests introduces the following challenges to a software development company:

• Unpredictable response times
• Rate limits imposed by third-party services
• Additional costs associated with excessive API calls

These factors can slow down tests and lead to intermittent failures due to network inconsistencies, hindering the test suite's reliability. To circumvent these issues, developers should avoid directly testing third-party integrations within E2E tests.

Playwright's Network API empowers developers to mock these external services. This approach involves simulating the behavior of third-party APIs, ensuring tests remain rapid and consistent regardless of the performance or availability of the real services.

test('POST /orders places an order', async ({ request }) => {
  await request.route('/payment-gateway/process', (route) => {
    route.fulfill({
      status: 200,
      body: '{"success": true}',
    });
  });

  const orderData = {
    items: [...],
    paymentInfo: [...],
  };

  const response = await request.post('/orders', orderData);
  expect(response.status()).toBe(201);
});

The provided code snippet showcases how to mock the behavior of a payment gateway API by intercepting requests directed to /payment-gateway/process. The mock response simulates a successful payment transaction, ensuring that the order placement functionality within the test remains isolated and unaffected by external dependencies.
Separate test suites can be established to compare mock data with actual API outputs for alignment verification. This approach balances the need to validate integration functionality with the requirement for rapid and reliable E2E tests.

Leverage Playwright's tooling

Script Creator provides an all-in-one package for simplifying the process of creating, running, and fixing tests. Thus, a software development company must leverage Playwrite's tooling:
Inspector: This in-built inspector empowers programmers to examine and fix test scripts by pausing the program at specific points. It helps move step-by-step through the code and inspect the output from the console.
UI mode: UI Mode is equipped with features that simplify the process of exploring, running, and troubleshooting tests. Such a feature allows developers to move back in time within the testing process. It is a wait-and-see mode for automatically re-executing tests after code updates and a detailed record of test progress.
Trace viewer: This tool helps pinpoint the source of test failures by offering details about each step. It also includes images of what was displayed on the page, the information sent over the network, and how the user interacted with the system.
Visual Studio Code add-on: Developers can make use of the Playwright add-on for VS Code. This allows them to create, execute, and debug tests directly from their preferred coding environment.
Code creator: Playwright's command line tool enables the creation of test scripts by capturing how users interact with a page. This is especially useful in the early stages of test case development.
TypeScript compatibility: Playwright is designed to be compatible with TypeScript, allowing developers to create and execute tests within TypeScript files. This can enhance type safety and integrate smoothly with their current coding practices.

Conclusion

This was an all-inclusive blog on the best practices of API testing using Playwrite. these practices, developers can build strong and reliable applications. Thus, a software development company can ensure a seamless and secure user experience.