Skip to content
Postman API Testing Tips

How To Automate Rest Api Testing Using Postman

API Testing Blog

Automating REST API Testing Using Postman: A Comprehensive Guide

Postman is a powerful tool that can be used to test REST APIs, and its automation capabilities allow you to streamline your testing process and ensure the quality of your APIs.

Getting Started with Postman for API Testing

1. Setup and Installation:

  • Install Postman: You can download and install Postman from their official website (https://www.postman.com/). It’s available as a desktop app for macOS, Windows, and Linux, and you can also use the Postman web app.
  • Create a workspace: Workspaces in Postman help organize your API testing activities and collaborate with others. You can create a new workspace on the Postman app and name it appropriately.

2. Building Your First API Request:

  • Access the API Documentation: Make sure you have access to the API documentation, which defines the endpoints, request methods, headers, and expected responses for each API call.
  • Create a New Request: On the Postman app, navigate to the “New Request” button.
  • Populate Request Details:
    • Request Method: Select the HTTP method (GET, POST, PUT, DELETE, PATCH, etc.).
    • URL: Enter the complete URL of the API endpoint.
    • Headers: Add any required headers based on the API documentation.
    • Body: For POST, PUT, and PATCH requests, enter the request body data in the appropriate format (JSON, XML, etc.).

Example:

API Endpoint: https://reqres.in/api/users Method: GET

// POSTMAN code
GET https://reqres.in/api/users

3. Sending the Request and Analyzing Results:

  • Send the request: Click the “Send” button in Postman.
  • Response: Postman will display the API response, including the status code, headers, and response body.
  • Validate the Response: Verify that the response status code is as expected (e.g., 200 for success, 400 for bad requests, etc.). Check the response headers and body for the expected data and formatting.

Automating API Tests with Postman Collections

1. Defining Collections and Environments:

  • Collections: Collections in Postman are groups of requests that you can organize and manage together. They represent a set of related API calls.
  • Environments: Environments allow you to store variables and settings that can be used across multiple requests within a collection. This helps maintain consistency and makes it easier to switch between different testing scenarios (e.g., testing against different environments, like development, staging, production).

2. Creating a Basic API Test Collection:

  • Create a New Collection: From the Postman interface, click “Create” and select “Collection”. Give it a suitable name, for example, “User API Tests”.
  • Add Requests: Add the requests for the API actions you’ll be testing. In Postman, you’ll see a “New request” option under each collection.
  • Define Environment Variables: Create a new environment for your tests. For example, use environment variables for base URLs, API keys, and other configuration settings.

Example:

Environment Name: “staging”

Environment Variables:

  • base_url: https://api.staging.example.com
  • api_key: YOUR_API_KEY

Request within the collection:

// POSTMAN code
GET {{base_url}}/users

3. Writing Test Scripts for Your Requests:

  • Test Scripts: Postman allows you to write JavaScript code (called “test scripts”) to perform assertions and validate the response data. This is crucial for automating checks beyond just the status code.
  • Using Assertions: In your test scripts, use Postman’s built-in assertion library to check conditions and make sure your API is functioning correctly.

Example:

// POSTMAN test script
pm.test("Status code is 200", function () {
    pm.response.to.have.status(200);
});


pm.test("Response contains expected data", function () {
    pm.expect(pm.response.json().data).to.be.an('array');
    pm.expect(pm.response.json().data.length).to.be.above(0);
});

Automating API Testing with Postman Runners

1. Running Your Collection:

  • The Runner: The Postman Runner allows you to execute collections of requests automatically and provides reports for your tests.
  • Selecting and Setting Up: Select the collection you want to run and choose the environment you want to use.
  • Data Files (Optional): To further automate your tests, you can use data files to provide input for your API calls. Data files can include CSV, JSON, or other formats.

2. Analyzing Test Results:

  • Reports and Insights: Postman Runner generates reports that display the status of each request, execution time, and the results of your test scripts.
  • Identifying Issues: Examine the error messages, failed assertions, or unexpected response data to pinpoint any bugs or inconsistencies in your API.

Advanced Techniques for API Testing

  • Dynamically Generating Data: Use Javascript code in your Pre-request scripts to generate random data for tests, creating more comprehensive test scenarios.
  • Mocking APIs: Use Postman’s mocking capabilities to simulate API responses while testing or when real endpoints are not available.
  • Chaining Requests: Chain requests together within a collection, where the response from one request can be used as input for the next.
  • Integrations: Postman integrates with various tools like CI/CD pipelines (like Jenkins or GitHub Actions), enabling you to run API tests as part of your automated build process.

Benefits of Automating API Testing

  • Increased Efficiency: Reduce manual effort, test faster, and free up time for more complex tasks.
  • Improved Accuracy: Automated tests reduce the risk of human errors and ensure consistency.
  • Early Bug Detection: Identify issues early in the development lifecycle, saving time and cost.
  • Regression Testing: Easily run tests repeatedly to ensure that new code changes don’t break existing functionality.
  • Better Documentation: Automated API testing often results in better-defined API documentation.

Conclusion:

Automating your REST API testing using Postman is a crucial step towards ensuring the quality of your APIs and the software that relies on them. By leveraging the power of Postman’s features, you can streamline your testing process, improve accuracy, and gain valuable insights into the health and performance of your APIs. Remember to start small, build upon your knowledge, and explore the advanced features of Postman to create robust and comprehensive API test automation solutions.

API Testing Blog