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How To Do Automation Testing Using Postman

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Automating API Testing with Postman: A Comprehensive Guide

Postman is a powerful tool, not just for exploring and testing APIs, but for automating those tests as well. This guide will cover the fundamentals of automating API tests using Postman, equipping you with the skills to build robust and maintainable test suites.

Understanding Postman Collections and Environments

Postman Collections are the cornerstone of automation. They allow you to group multiple API requests into logical units, making it easier to manage and organize your tests. Environments, on the other hand, provide a way to store variables that can be dynamically substituted into your requests, facilitating data-driven testing.

Example: Creating a Collection for User Authentication:

  1. Create a New Collection: Click the “New” button and select “Collection”. Name it “User Authentication”.
  2. Add Requests: Within the collection, add two requests: “Signup” and “Login”.
  3. Define Environment Variables: Go to “Manage Environments” (icon of a globe) and create a new environment called “Test”. Add variables like “baseUrl”, “username”, “password” etc., with placeholder values.

Writing Automated Tests with Postman’s Test Scripting

The magic of Postman automation lies in its scripting capabilities. You can write test scripts using JavaScript to assert the expected behavior of your API responses.

Example: Testing Response Status Codes:

  1. Add a Test Tab: In the “Signup” request, click the “Tests” tab.
  2. Write a Test Script: Add the following script: 
    pm.test("Status code is 201", function () {
        pm.response.to.have.status(201);
    });
  3. Explanation: The script tests if the “Signup” request returns a status code of 201 (Created).

Implementing Data-Driven Testing

Postman’s power is amplified by its ability to work with data sources. This allows you to run your tests with multiple sets of data, ensuring comprehensive coverage.

Example: Data-Driven User Registration:

  1. Create a Data File: Save a JSON file named “users.json” containing user data (e.g., usernames, passwords) in an array format.
  2. Incorporate Data in Requests: In the “Signup” request, click the “Body” tab and select “raw” format. Paste the following code to dynamically access data from the file: 
    {
        "username": "{{user.username}}",
        "password": "{{user.password}}"
    }
  3. Select Data Source: In the “Run” section, choose “Data” and select “users.json”.
  4. Run Tests: When you execute the collection, Postman will iterate through the data file, sending each user’s information to the “Signup” request, effectively testing multiple registration scenarios.

Working with Assertions and Validations

Postman provides a comprehensive set of assertions for validating API responses. You can check response bodies, headers, status codes, and more.

Example: Validating a Successful Login Response:

  1. Add a Test Script in the “Login” Request: 
    pm.test("Validating response body", function() {
        pm.response.to.have.jsonBody("message", "Login successful");
    });
  2. Explanation: The test script checks if the “Login” response contains the message “Login successful” in the JSON body.

Running and Managing Automated Tests

Once your tests are written, you can run them individually, but the real power lies in running them as a suite.

How to Execute Tests:

  1. Run Collection: Click the “Run” button on the collection to execute all the requests and tests within it.
  2. Monitor Results: The results of each request and test will be displayed, providing an overview of successes and failures.

Integrating Postman with CI/CD Pipelines

The ultimate goal is to integrate Postman tests into your Continuous Integration and Continuous Delivery (CI/CD) pipelines for automated testing in every build.

Considerations for CI/CD Integration:

  1. Postman CLI: The command-line interface allows you to run collections and tests directly from your CI/CD pipeline.
  2. Newman: A command-line tool for running Postman collections, ideal for scripting and integrating with CI/CD tools.
  3. Postman API: Postman offers APIs for programmatically accessing and managing your collections, environments, and tests.

Conclusion

Postman emerges as a powerful tool for API testing automation, enabling you to build comprehensive and effective test suites. By leveraging collections, environments, and testing scripts, you can create robust and maintainable automated workflows. With features like data-driven testing and CI/CD integration, Postman empowers you to ensure the quality and reliability of your APIs. This comprehensive guide has equipped you with the knowledge and practical examples to begin automating your API testing using Postman.

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