Rohit Kakade
Written By Rohit Kakade Sr. QA Engineer

API Automation Testing With Postman

post date
February 22, 2024
API Automation Testing With Postman
Reading Time: 9 minutes

APIs (Application Programming Interfaces) serve as the backbone of modern software applications, enabling seamless communication and data exchange between different systems. As the complexity of software projects grows, so does the importance of efficient API development and rigorous testing.

Postman, a versatile API development and testing tool, offers a comprehensive suite of features designed to streamline these processes. In this detailed guide, we’ll take you through each step of mastering API development and testing with Postman, empowering you to optimize your workflows and ensure the reliability of your APIs.

Step 1: Installing Postman

1. Visit the Postman Website: Start by navigating to the Postman website.

2. Download and Install: Choose the appropriate version of Postman for your operating system (Windows, macOS, or Linux) and follow the installation instructions provided. Postman also offers a web-based version for those who prefer not to install software locally.

Step 2: Getting Started with Postman

1. Launch Postman: Once the installation is complete, launch the Postman application from your desktop or browser.

2. Sign In or Create Account: Sign in with your existing Postman account to sync your data across devices or create a new account if you don’t have one.

3. Interface Familiarisation: Take some time to explore the Postman interface. Familiarise yourself with the main components such as the sidebar navigation, request builder, response viewer, and other tabs like “Collections,” “History,” “Runner,” and “Settings.”

Step 3: Creating Your First Request

1. Initiate a New Request: Click on the “New” button located at the top left corner of the interface to create a new request.

2. Choose HTTP Method: Select the appropriate HTTP method (GET, POST, PUT, DELETE, etc.) from the dropdown menu.

3. Enter API Endpoint: In the request URL field, enter the URL of the API endpoint you want to interact with. You can also specify query parameters if necessary.

4. Optional Parameters and Headers: Add any required parameters, headers, or request body to your request. Postman provides intuitive controls to input and manage these elements.

5. Send and View Response: Click on the “Send” button to execute the request. Postman will display the response in the response viewer below, including status codes, headers, and response body.

The table below presents a comparison of various HTTP methods.

Comparison of HTTP Method

Step 4: Organising Requests with Collections

1. Access Collections Tab: Navigate to the “Collections” tab on the left sidebar within Postman.

2. Create a New Collection: Click on the “New Collection” button and give your collection a descriptive name, such as “User API” or “Product Endpoints.”

3. Add Requests to Collection: Use the “Add Request” button to add individual requests to your collection. Organize them logically based on their purpose or functionality.

4. Utilise Folders for Organization: Within collections, create folders to further organize related requests. For example, you might create folders for different API versions or categories of endpoints.

Step 5: Managing Environments

Managing environments in Postman allows you to streamline API testing under different configurations. Follow these steps to effectively manage environments:

1. Access Environment Settings: Click on the gear icon located in the top right corner of the Postman interface and select “Manage Environments.”

2. Create a New Environment: Click on the “Add” button to create a new environment. Give your environment a descriptive name, such as “Development,” “Testing,” or “Production.”

3. Define Environment Variables: Within the environment settings, define environment-specific variables such as base URLs, authentication tokens, or other dynamic values. These variables can be reused across multiple requests.

4. Reference Environment Variables: In your requests, reference these environment variables by encapsulating them within double curly braces. For example, `{{baseURL}}/api/users` will be replaced with the actual base URL defined in your environment.

5. Switch Between Environments: Easily switch between environments using the dropdown menu in the top right corner of the Postman interface. This allows you to test your API under different configurations without the need for manual modifications.

Step 6: Writing Test Scripts

Writing test scripts in Postman enables you to automate the validation of API responses. Follow these steps to write and execute test scripts:

1. Access Test Scripts: After sending a request, navigate to the “Tests” tab within the request editor.

2. Write Test Scripts: Write test scripts using JavaScript to define the desired validation logic. You can access various parts of the response object and perform assertions to verify aspects such as status codes, response bodies, or specific data fields.

3. Utilise Assertions: Utilise built-in assertion functions provided by Postman to verify the expected behavior of your API. Common assertion functions include `pm.expect()` for simple checks and `pm.test()` for more complex scenarios.

4. Execute Test Scripts: Click on the “Send” button again to execute the request along with the defined test scripts. Postman will run the tests and display the results within the “Test Results” tab, indicating whether each test passed or failed.

Step 7: Automating Tests with Newman

Newman, Postman’s command line interface (CLI) tool, enables you to automate API testing as part of your CI/CD pipeline. Follow these steps to automate tests using Newman:

1. Install Newman: Install Newman by following the installation instructions provided here.

2. Export Postman Collection: Export your Postman collection as a JSON file from the Postman interface. This file contains all the requests, tests, and configurations defined within your collection.

3. Run Newman: Open your terminal or command prompt and run Newman with the exported collection file as input. For example: `newman run myCollection.json`.

4. Review Test Results: Newman will execute the collection and provide detailed test results, including the number of tests passed, failed, and skipped. These results can be integrated into your CI/CD pipeline to ensure the reliability of your APIs with each deployment.

Step 8: Documenting Your APIs

Documenting your APIs is crucial for ensuring clarity and facilitating collaboration among team members. Follow these steps to document your APIs effectively using Postman:

1. Navigate to the Collection: Within Postman, navigate to the collection you wish to document.

2. Generate Docs: Click on the three dots next to the collection name and select “Generate Docs” from the dropdown menu.

3. Customise Settings: Customise the documentation settings according to your preferences, including the format, styling, and additional details you want to include.

4. Generate Documentation: Once you’ve configured the settings, click on the appropriate button to generate the documentation. Postman will generate a documentation page based on your collection, which you can then share with stakeholders for reference.

Step 9: Collaborating with Team Members

Collaboration is key to successful API development and testing. Here’s how you can collaborate with team members using Postman:

1. Share Collections and Environments: Share your collections and environments with team members by clicking on the “Share” button within Postman.

2. Set Sharing Permissions: Choose the appropriate sharing settings, such as read-only or read-write access, to control collaboration permissions based on your team’s needs.

3. Work Together: Collaborate with team members on API development and testing tasks by working together within Postman. Leverage shared collections and environments to ensure consistency and efficiency across the team.

Step 10: Continuous Monitoring and Improvement

Continuous monitoring and improvement are essential for maintaining the quality and reliability of your APIs. Follow these steps to ensure continuous monitoring and improvement:

1. Set Up Postman Monitoring: Set up Postman Monitoring to track API performance and uptime. This allows you to identify and address any performance issues or reliability concerns proactively.

2. Regular Monitoring: Monitor critical API endpoints regularly to identify any deviations from expected performance or behavior.

3. Review and Refine: Continuously review and refine your API workflows based on monitoring insights and feedback from stakeholders. Identify areas for improvement and implement changes to enhance the overall quality of your APIs.

Step 11: Manipulating Cookies

When testing APIs, cookies play a significant role in maintaining state and session management. In Postman, you can manipulate cookies during API testing using JavaScript in the “Tests” tab. Here’s a more detailed approach:

1. Understand Cookie Manipulation: Cookies are often used for authentication, session management, and tracking user behavior. Understanding how cookies work and their significance in API testing is crucial.

2. Accessing Cookies: After sending a request in Postman, navigate to the “Tests” tab within the request editor. Here, you can access and manipulate cookies using JavaScript.

3. Setting Cookies: Use JavaScript code to set cookies in the response of a request. For example, you can extract cookies from the response headers and set them in the request headers for subsequent requests.

4. Extracting Cookies: Similarly, you can extract cookies from the response of a request using JavaScript. This allows you to capture session tokens or other important information for further testing.

5. Managing Cookie Expiry and Domain: Pay attention to cookie expiration dates and domain settings, as these can affect the behavior of your API requests. Make sure to handle cookies appropriately based on your testing requirements.

Step 12: Efficient Header Management

Efficient header management is essential for maintaining consistency and reusability across multiple requests in Postman. Here’s a detailed approach to achieving efficient header management:

1. Utilise Collections: Group related requests into collections based on functionality or API endpoints. This helps in organizing your requests and managing headers more efficiently.

2. Global Variables: Define global variables for commonly used headers such as authentication tokens, content types, or user agents. This allows you to reuse these headers across multiple requests within the same collection.

3. Environment Variables: Use environment variables to manage headers that may vary across different environments, such as base URLs or API keys. By defining environment-specific variables, you ensure that your requests are adaptable to different testing environments.

4. Dynamic Headers: Use scripting in the “Pre Request Script” tab to dynamically generate headers based on specific conditions or inputs. This allows for more flexibility and customization in your header management approach.

5. Documentation and Naming Conventions: Document your headers and their purpose within your collections to ensure clarity and maintainability. Follow consistent naming conventions to make it easier for team members to understand and use the headers.

Step 13: Accessing API History

Postman maintains a comprehensive history of API requests, allowing you to review and rerun past requests as needed. Here’s how to access and leverage API history effectively:

1. Access History: In the Postman interface, navigate to the “History” tab to access the list of recent API requests that you’ve made.

2. Filtering and Search: Use filtering and search functionalities to quickly find specific requests based on URLs, methods, or other criteria. This helps in navigating through large volumes of API history more efficiently.

3. Reviewing Responses: Review the responses of past requests to analyze the behavior of your APIs over time. This can help in identifying patterns, trends, or potential issues that may require further investigation.

4. Rerunning Requests: Easily rerun past requests from the history tab to verify changes, debug issues, or perform regression testing. This allows you to quickly validate the functionality and integrity of your APIs.

Step 14: Leveraging Environment Variables

Environment variables in Postman provide a powerful mechanism for making your requests more adaptable and parameterized across different environments. Here’s how to leverage environment variables effectively:

1. Understanding Environment Variables: Environment variables allow you to define dynamic values that can be used across multiple requests within a specific environment.

2. Defining Environment Variables: Define environment variables for elements that may vary across different environments, such as base URLs, API keys, or authentication tokens.

3. Managing Environments: Utilise Postman’s environment management capabilities to create and switch between different environments, such as development, testing, and production.

4. Reference Environment Variables: Reference environment variables within your requests by encapsulating them within double curly braces. This allows you to dynamically adjust request parameters based on the selected environment.

5. Environment Inheritance: Leverage environment inheritance to inherit variables from parent environments, reducing duplication and ensuring consistency across environments.

Step 15: Writing Test Scripts with Chai Assertions

Writing test scripts with Chai assertions allows you to perform more advanced validations on API responses. Chai is a popular assertion library for JavaScript, providing a wide range of assertion styles. Here’s how to enhance your test scripts with Chai assertions:

1. Importing Chai Library: Ensure that the Chai Library is available in your Postman environment. You can import Chai via a CDN link or by including it directly in your test scripts.

2. Writing Assertions: Use Chai’s expressive assertion syntax to write meaningful and descriptive assertions. Assertions can cover various aspects of the API response, including status codes, response bodies, headers, and more.

3. Assertion Styles: Choose the assertion style that best suits your testing needs, such as BDDstyle assertions (expect/should) or TDDstyle assertions (assert). Familiarise yourself with Chai’s documentation to understand the available assertion styles and methods.

4. Handling Asynchronous Tests: If your API tests involve asynchronous operations, make sure to handle them appropriately using Chai’s asynchronous assertion capabilities. This ensures that your tests wait for asynchronous operations to complete before making assertions.

5. Error Handling: Implement error handling in your test scripts to gracefully handle assertion failures. This allows you to provide informative error messages and debug failing tests more effectively.

Step 16: Running Automated Test Cases with Newman

Newman is Postman’s command line interface (CLI) tool, designed for running automated test cases outside of the Postman app. Here’s how to explore the advanced features of Newman for seamless automation of API testing:

1. Installation: Install Newman by following the installation instructions provided on the Postman website or GitHub repository.

2. Export Postman Collection: Export your Postman collection as a JSON file from the Postman interface. This file contains all the requests, tests, and configurations defined within your collection.

3. Running Tests with Newman: Open your terminal or command prompt and run Newman with the exported collection file as input. Specify additional options such as environment variables, reporters, or iteration counts as needed.

4. Integrating with CI/CD Pipelines: Integrate Newman into your CI/CD pipeline for automated testing as part of your software development lifecycle. Configure your pipeline to trigger Newman runs on code changes or deployments, ensuring continuous validation of your APIs.

5. Analysing Test Results: Analyse the test results generated by Newman to identify any failures or issues. Newman provides detailed reports and exit codes, allowing you to pinpoint the root cause of failures and take appropriate action.

Conclusion

In summary, mastering API development and testing with Postman is crucial for QA professionals to ensure the quality, reliability, and performance of software products.

Through fundamental steps like installing Postman, creating requests, and organizing collections, QA teams can efficiently design and execute test cases. Advanced techniques such as manipulating cookies, managing headers, and leveraging environment variables enable thorough testing and validation across various scenarios.

By utilizing Postman’s capabilities effectively, QA professionals can streamline workflows, collaborate with development teams, and deliver high-quality software that meets user expectations.

Rohit Kakade
Written By Rohit Kakade Sr. QA Engineer

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