Automating API Testing with Postman

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As web applications become increasingly complex, the need for robust and efficient API testing has never been more critical. Postman, a popular API testing tool, offers a user-friendly interface and powerful automation capabilities that enable developers and testers to streamline their testing process. This article will walk you through a comprehensive guide on automating API testing with Postman.

But before that, please ensure you have installed the Postman and learned all the elements inside it. If not, kindly refer to our previous articles on Postman installation and testing APIs in Postman.

Table of contents

• Creating a Postman collection
• Setting up environment variables
• Writing test scripts
• Running single request and collection
• Setting up automated test runs
• Manual vs. automated API testing
• Conclusion

Creating a Postman collection

• Click New in the top-left corner and select Collection. Give your collection a name and click Create Collection.

• Click the Add Request button in the newly created collection. Enter a request name and the API endpoint URL. Choose the appropriate HTTP method (GET, POST, PUT, DELETE, etc.), and if needed, add request parameters, headers, and request body.

Refer to our Postman Collections guide for more details.

Setting up environment variables

• Click on the Environment Quick Look icon in the top-right corner. Give your environment a name and click Add.

• Add the variables required for API testing in the newly created environment. For example, you can add base_url, access_token, or any other parameters needed for your requests.

• Click the Save button to save the environment variables.

Writing test scripts

• Postman test scripts allow you to define assertions and validations for your API responses. These scripts are written in JavaScript.
• In your request, click on the Tests tab. Here, you can write your test script to check the response status code, response time, or the presence of specific elements in the response body. For example:

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

pm.test("Response time is less than 200ms", function () {
    pm.expect(pm.response.responseTime).to.be.below(200);
});

pm.test("Response contains valid data", function () {
    pm.response.to.have.jsonBody('data', {
        id: 123,
        name: 'John Doe',
        email: 'john@automateNow.io'
    });
});

Running single request and collection

• Click the Send button in the request window to execute a single request. Postman will send the request, and the test results will be displayed in the Test Results pane at the bottom.

• To run the entire collection, click on the Runner button. Choose the desired environment, and Postman will execute each request in the collection sequentially. Refer to our Postman collection runner for more details.

Setting up automated test runs

• If you have tests that apply to the entire collection, you can create collection-level test scripts. To do this, click on the three dots next to the collection name and select Edit. In the Tests tab, write your collection-level test scripts.
• Newman is a command-line tool that allows you to run Postman collections from the terminal or command prompt. Install Newman globally by running the following command:

npm install -g newman

• Once Newman is installed, navigate to your collection’s folder and run the following command:

newman run your_collection_name.json -e your_environment_name.json

Replace your_collection_name.json and your_environment_name.json with the names of your collection and environment files. Check out our Postman Newman detailed guide to learn more.

Manual vs. automated API testing

Manual API testing in Postman

• Human Intervention: Manual API testing requires a tester to interact with Postman actively. Each test case is executed manually by sending requests and examining responses.
• Time-Consuming: As the number of test cases increases, manual testing becomes time-consuming and labor-intensive. Testers need to perform repetitive tasks, leading to potential human errors.
• Limited Coverage: With manual testing, achieving extensive test coverage is challenging, especially for large-scale applications with numerous APIs.
• Prone to Human Errors: Human errors, such as incorrect data entry or misinterpretation of test results, may impact the accuracy and reliability of the testing process.

Automated API testing with Postman

• Unattended Execution: Automated API testing eliminates the need for continuous human intervention. Test cases are executed automatically using scripts, saving time and effort.
• Improved Efficiency: Automated testing allows for faster execution of test cases, enabling rapid feedback on API changes and reducing the overall testing cycle.
• Comprehensive Test Coverage: Automation enables testers to create and execute many test cases, improving test coverage across APIs.
• Accuracy and Consistency: Automated tests ensure consistent execution, reducing the risk of human errors and enhancing the reliability of test results.

Final thoughts on automating API testing with Postman

Automating API testing with Postman provides significant advantages over manual testing. By leveraging Postman’s automation capabilities, testers can execute test cases efficiently, achieve comprehensive test coverage, and maintain consistent and accurate results. The transition from manual to automated API testing empowers development teams to deliver high-quality applications faster, making Postman an indispensable tool in modern software development. Happy testing!

This post is part of our comprehensive Postman Mini-Course.