Automating API Testing

# CHAPTER 14

Automating API Testing #

1. Introduction #

2. Learning Objectives #

• Understand the concept of test suites and automated test flows.

• Use the Postman Collection Runner to execute an entire folder of requests.

• Use JavaScript to extract a variable from one response and use it in the next request (Chaining).

• Understand the basics of Newman for CI/CD integration.

3. Beginner-Friendly Explanation #

The Collection Runner is the conveyor belt for your API requests. You place your requests in order: Create User -> Get User -> Update User -> Delete User. You press one button called "Run". Postman fires them off automatically in sequence, running the tests for each one, and hands you a beautiful final report showing exactly which steps passed and which failed.

4. Real-World Examples #

• The Login Flow: Request 1 sends an email and password. The test script grabs the token from the response and saves it as an environment variable. Request 2 uses that variable to fetch the user's profile. You cannot run Request 2 without running Request 1 first!

• Data Teardown (Cleanup): A QA engineer runs tests that create 10 dummy users in the database. The final request in the collection is an automated "Delete All Dummy Users" call to keep the staging database clean.

5. Step-by-Step Tutorial (The Collection Runner) #

1. 1. Hover your mouse over the User Workflow folder in the left Sidebar.

1. 2. Click the three dots ... and select Run folder (or click the folder and click the "Run" button in the top right).

1. 3. The Runner tab opens.

1. 4. You will see a list of your three requests. You can drag and drop to reorder them if needed.

1. 5. On the right panel, you can choose "Iterations" (how many times to loop the whole process) and "Delay" (pause between requests).

1. 6. Click the big blue Run User Workflow button.

1. 7. Watch as Postman executes them sequentially and generates a visual report of your PASS / FAIL tests!

6. Passing Data Between Requests (Chaining) #

In Request 1 (Create User) - Tests Tab:

// 1. Check if creation succeeded
pm.test("Status code is 201", function () {
    pm.response.to.have.status(201);
});

// 2. Extract the newly created ID from the JSON response
const responseData = pm.response.json();
const newUserId = responseData.id;

// 3. Save it dynamically to an Environment Variable!
pm.environment.set("temp_user_id", newUserId);

In Request 2 (Read User) - URL Bar:

https://api.example.com/users/{{temp_user_id}}

*Magic! Request 2 automatically knows the ID generated by Request 1.*

7. Introduction to Newman (Command Line) #

How it works:

1. 1. You export your Postman Collection as a JSON file.

1. 2. You run a simple command in your terminal:

1. 3. Newman executes all the requests and prints a beautiful text-based test report right in your terminal. This is the foundation of CI/CD (Continuous Integration / Continuous Deployment).

8. Controlling the Flow (Advanced) #

if (pm.response.code !== 201) {
    // Stop the entire collection runner
    postman.setNextRequest(null); 
} else {
    // Jump to a specific request by name
    postman.setNextRequest("Update User Profile");
}

9. Best Practices #

• Clean State: A good automated test suite should leave the database exactly how it found it. If your suite creates data, the final request in the suite should delete that data.

• Use Delays: If you are testing a live production API, running 50 requests in 1 second might trigger the API's Rate Limiter, causing your tests to fail with a 429 Too Many Requests error. Add a 500ms delay in the Runner settings.

10. Common Mistakes #

• Order of Execution: The Runner executes based on the order in the Sidebar. If you accidentally drag "Delete User" to the top of the folder, it will run first and fail, causing the rest of the flow to break.

• Forgetting to save: The Collection Runner uses the *saved* state of your requests. If you edit a test script but forget to press Ctrl+S, the Runner will execute the old version of the script!

11. Mini Exercises #

1. 1. Locate the button to open the Collection Runner in your Postman interface.

1. 2. What JavaScript command do you use to save a dynamic value into an environment variable during a test script?

12. Coding/Testing Challenges #

13. MCQs with Answers #

14. Interview Questions #

• Q: Explain the concept of "Request Chaining" in Postman. How do you implement it?

• Q: What is Newman, and why would an engineering team choose to use it over the Postman GUI desktop app?

• Q: Explain the purpose of postman.setNextRequest().

15. FAQs #

16. Summary #

17. Next Chapter Recommendation #