Response time assertions in Postman - Build an Automation Script

Verify API response time is under 500 milliseconds

Preconditions (2)

Step 1: Open Postman and create a new GET request

Step 2: Enter the API endpoint URL in the request URL field

Step 3: Send the request by clicking the Send button

Step 4: Observe the response time shown in Postman

Step 5: Verify that the response time is less than 500 milliseconds

✅ Expected Result: The API responds successfully and the response time is less than 500 milliseconds

Automation Requirements - Postman Tests (JavaScript)

Assertions Needed:

Response status code is 200

Response time is less than 500 milliseconds

Best Practices:

Use pm.response.to.have.status for status code assertion

Use pm.expect(pm.response.responseTime).to.be.below(500) for response time assertion

Write clear and simple test scripts inside the Tests tab

Avoid hardcoding values except for thresholds like 500 ms

Automated Solution

Postman

pm.test('Status code is 200', () => {
    pm.response.to.have.status(200);
});

pm.test('Response time is less than 500 ms', () => {
    pm.expect(pm.response.responseTime).to.be.below(500);
});

The first test checks that the API returns a status code 200, which means success.

The second test checks that the response time is below 500 milliseconds using pm.response.responseTime.

Both tests use Postman's built-in pm object and chai assertion library for clear and readable assertions.

This script should be placed in the Tests tab of the Postman request.

Common Mistakes - 3 Pitfalls

Checking response time with incorrect property like pm.response.time

Using hardcoded status codes without assertion methods

{'mistake': 'Not placing the test script inside the Tests tab', 'why_bad': "Scripts outside the Tests tab won't run after the request, so no assertions happen.", 'correct_approach': 'Always write test scripts inside the Tests tab of the Postman request.'}

Bonus Challenge

Now add data-driven testing with 3 different API endpoints and verify each response time is under 500 ms

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