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How To Use Postman Interceptor With Native App

API Testing Blog

Leveraging Postman Interceptor for Native App Testing

Postman Interceptor is a powerful tool that allows you to intercept and manipulate network traffic between your native app and the backend server. This capability is invaluable for API testing, offering a flexible and efficient way to test your app’s interactions with the API.

1. Understanding Postman Interceptor

Postman Interceptor is a Chrome extension that acts as a proxy between your native app and the backend server. When it’s enabled, all network requests made by your app pass through Interceptor, giving you the ability to:

  • Inspect Requests and Responses: View the details of each request and response, including headers, body, and status code.
  • Modify Requests: Change the request method, headers, body, or URL before the request is sent to the server.
  • Mock Responses: Generate fake responses to simulate different server behaviors, even without a backend server in place.
  • Record Requests: Capture and save requests for later use in Postman.

2. Install and Configure Postman Interceptor

  1. Install Postman Interceptor: Download and install the Postman Interceptor extension from the Chrome Web Store.
  2. Enable Interceptor: Open your browser and navigate to chrome://extensions. Enable the Postman Interceptor extension.
  3. Configure Proxy Settings:
    • Android: Open the developer options in your Android device (usually accessed by repeatedly tapping “Build Number” in Settings > About phone). Enable “USB debugging” and “Select USB Debugging App” and choose “Postman Interceptor.”
    • iOS: iOS doesn’t have built-in proxy settings. You’ll need to use a third-party app like “Proxyman” to configure a local proxy for your iOS device.

3. Interacting with Requests and Responses

Once you’ve installed and configured Interceptor, you can begin interacting with your app’s network traffic:

  1. Launch your Native App: Start your native app and perform actions that generate network requests.
  2. View Network Traffic: Interceptor will capture the requests and responses. You can view them in Interceptor’s interface, which shows a list of requests with details like method, URL, and response status.
  3. Inspect Request/Response Details: Click on a request to view its full details, including headers, body, and response time.
  4. Modify Requests (For Testing and Debugging): You can modify request parameters like headers, URLs, or the request body by clicking on the “Modify” button.
  5. Mock Responses (Simulate Backend Behavior): You can create mock responses for specific endpoints to simulate different server scenarios. This is useful for testing how your app handles various server conditions without requiring a real backend service.

Example: Modifying a Request Header:

Let’s say you have a login endpoint in your app. You can modify the request header in Interceptor to add a custom token for authenticated requests:

  1. Intercept the Login Request: Capture the login request in Interceptor.
  2. Modify the Header: Click the “Modify” button and add a new header named “Authorization” with a value of your choice (e.g., “Bearer your_token”).
  3. Send the Modified Request: Interceptor will send the modified request to the server.

4. Recording and Exporting Requests

If you’re testing APIs for a specific project, recording and exporting your requests simplifies your testing process.

  1. Record Requests: Enable the “Record” option in Postman Interceptor, which will capture all network requests and save them.
  2. Export Requests: Once you’ve recorded some requests, you can click on the “Export” button to save them as a JSON file.
  3. Import into Postman: Import the saved JSON file into Postman to easily manage and reuse your recorded requests for API testing.

Example: Recording and Exporting Requests for Login:

  1. Enable Recording: Toggle the “Record” button in Interceptor.
  2. Login to Your App: Perform a login action in your app.
  3. Export Requests: Click on the “Export” button in Interceptor to save the captured requests as a JSON file.

5. Best Practices for Using Postman Interceptor

  • Avoid Interfering with Real User Traffic: Use Interceptor only for testing and debugging. Avoid using it on production environments or when testing scenarios that involve sensitive user data.
  • Clear Interceptor History: Regularly clear the captured requests and responses in Interceptor’s history to prevent data accumulation and potential security risks.
  • Use Mock Responses Carefully: While mock responses are a powerful tool for testing, they should not replace testing with real backend data. Use mock responses to simulate specific scenarios, but always test your app with actual data when possible.
  • Combine with Postman Collections: Use Interceptor to capture requests and create Postman collections. This allows you to efficiently manage and organize your API tests.

Conclusion:

Postman Interceptor is a valuable tool for testing native apps, allowing you to intercept and manipulate network traffic. By using it effectively, you can streamline your API testing process, improve your app’s quality, and identify potential issues. Remember to use it responsibly and combine it with other Postman features for a comprehensive testing workflow.

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