How to Check if a Field is Returning Null in Postman Automation

How to Check if a Field is Returning Null in Postman Automation

21 May 2024 Stephan Petzl Leave a comment Tech-Help

When working with API testing in Postman, it’s common to encounter scenarios where you need to verify if a specific field in the response is null. This can be challenging, especially when the field might also return other falsy values like 0 or an empty string. Here’s a step-by-step guide to help you set up a robust check for null values.

Using Postman’s Built-in Functions

Postman provides built-in functions that make it easier to write tests for your API responses. Below is a method that ensures the field is checked accurately:

pm.test("Check if value is null", function() {
  var jsonData = pm.response.json();

This method uses Postman’s pm.expect function to check if the specified field is not undefined. This is effective because Postman references non-existent paths as undefined, not null.

Alternative Methods

If the above method doesn’t fit your specific needs, here are some alternative approaches you can consider:

Checking for Null Directly


This method directly checks if the field equals null. However, it may not handle cases where the field is undefined.

Checking for Undefined


This method validates that a fake JSON path is undefined, which can be useful for ensuring that non-existent fields are correctly identified.

Practical Example

Let’s consider a practical example where you are testing an API that returns user data. You want to ensure that the email field is not null or undefined.

pm.test("Check if email is not null", function() {
  var jsonData = pm.response.json();

This script will ensure that the email field in the response is neither null nor undefined, making your test more robust.

Enhancing Your Testing with Repeato

While Postman is a powerful tool for API testing, integrating your tests into a comprehensive test automation strategy can provide even greater benefits. This is where Repeato comes in. Repeato is a no-code test automation tool for iOS and Android that helps you create, run, and maintain automated tests for your apps.

Repeato’s intuitive test recorder and scripting interface allow you to automate complex use cases quickly. It also supports testing websites inside an Android emulator or device, making it a versatile tool for your testing needs. With explicit web testing support coming soon, Repeato will further streamline your testing processes.

For more information on how Repeato can enhance your testing strategy, visit our documentation page.

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