Response time in Postman - Build an Automation Script

Verify API response time is under 2 seconds

Preconditions (2)

Step 1: Open Postman and create a new GET request

Step 2: Enter the API endpoint URL: https://api.example.com/data

Step 3: Send the request by clicking the Send button

Step 4: Observe the response time displayed in Postman

✅ Expected Result: The response time should be less than 2000 milliseconds (2 seconds)

Automation Requirements - Postman test scripts

Assertions Needed:

Response time is less than 2000 ms

Best Practices:

Use pm.response.responseTime to get response time

Write clear assertion messages

Keep test scripts simple and readable

Automated Solution

Postman

pm.test('Response time is less than 2000 ms', function () {
    pm.expect(pm.response.responseTime).to.be.below(2000);
});

This script uses Postman's built-in pm object to access the response time of the API call.

The pm.test function defines a test with a clear name.

Inside, pm.expect checks that the response time is below 2000 milliseconds.

This ensures the API responds quickly enough, and the test will pass or fail accordingly.

Common Mistakes - 3 Pitfalls

Using hardcoded response time values without checking actual response

Not adding assertion messages

{'mistake': 'Checking response time in the request body or headers instead of using pm.response.responseTime', 'why_bad': 'Response time is not part of response data; it is a separate metric.', 'correct_approach': "Use Postman's responseTime property to measure response duration."}

Bonus Challenge

Now add data-driven testing with 3 different API endpoints to verify their response times

Show Hint

Practice

1. What does pm.response.responseTime represent in Postman?

easy

A. The time taken by the server to respond to a request

B. The size of the response body in bytes

C. The HTTP status code of the response

D. The number of requests sent in a collection

Solution

1. Step 1: Understand the meaning of response time

   Response time measures how fast a system replies to a request.

2. Step 2: Identify what pm.response.responseTime returns

   In Postman, pm.response.responseTime gives the time in milliseconds the server took to respond.

3. Final Answer:

   The time taken by the server to respond to a request -> Option A

4. Quick Check:

   Response time = server reply speed [OK]

Hint: Remember responseTime measures speed, not size or status [OK]

Common Mistakes:

• Confusing response time with response size
• Thinking it returns HTTP status code
• Assuming it counts number of requests

2. Which of the following is the correct syntax to assert that response time is less than 500ms in Postman test script?

easy

A. pm.test('Response time is less than 500ms', () => pm.response.responseTime < 500);

B. pm.test('Response time is less than 500ms', () => pm.expect(pm.response.responseTime).to.equal(500));

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

D. pm.test('Response time is less than 500ms', () => pm.response.responseTime > 500);

Solution

1. Step 1: Recall Postman assertion syntax

   Postman uses pm.test with a callback and pm.expect for assertions.

2. Step 2: Check correct assertion for less than 500ms

   The correct way to check if response time is below 500 is pm.expect(pm.response.responseTime).to.be.below(500).

3. Final Answer:

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

4. Quick Check:

   Use pm.expect(...).to.be.below(value) for less than [OK]

Hint: Use pm.expect(...).to.be.below(value) for less than checks [OK]

Common Mistakes:

• Using direct comparison without pm.expect
• Using > instead of < for less than
• Using to.equal instead of to.be.below

3. Consider this Postman test script snippet:

pm.test('Check response time', () => {
  pm.expect(pm.response.responseTime).to.be.below(300);
});

If the actual response time is 350ms, what will be the test result?

medium

A. Test will pass because 350 is below 300

B. Test will be skipped automatically

C. Test will error due to syntax mistake

D. Test will fail because 350 is not below 300

Solution

1. Step 1: Understand the assertion condition

   The test expects response time to be below 300ms.

2. Step 2: Compare actual response time with condition

   Actual response time is 350ms, which is greater than 300ms, so the condition fails.

3. Final Answer:

   Test will fail because 350 is not below 300 -> Option D

4. Quick Check:

   350 > 300 means test fails [OK]

Hint: Compare actual value with assertion condition carefully [OK]

Common Mistakes:

• Assuming test passes if value is greater
• Confusing below with above
• Thinking syntax error causes failure

4. You wrote this Postman test:

pm.test('Response time test', () => {
  pm.expect(pm.response.responseTime).to.be.lessThan(400);
});

But the test always errors out. What is the likely problem?

medium

A. You should use pm.response.time instead of pm.response.responseTime

B. The method lessThan is not valid in Postman assertions

C. The test needs to be inside a pm.response.to block

D. The response time cannot be tested in Postman

Solution

1. Step 1: Check Postman assertion methods

   Postman uses Chai assertion library where the correct method is below, not lessThan.

2. Step 2: Identify the invalid method causing error

   Using lessThan causes a syntax error because it is not recognized.

3. Final Answer:

   The method lessThan is not valid in Postman assertions -> Option B

4. Quick Check:

   Use .to.be.below() not .lessThan() [OK]

Hint: Use .to.be.below() for less than, not .lessThan() [OK]

Common Mistakes:

• Using unsupported assertion methods
• Confusing property names for response time
• Thinking response time tests are unsupported

5. You want to fail a Postman test if the response time is more than 200ms but allow up to 300ms with a warning message. Which test script correctly implements this?

hard

A. pm.test('Response time check', () => {
if(pm.response.responseTime > 300) {
pm.expect.fail('Response time too high');
} else if(pm.response.responseTime > 200) {
console.warn('Warning: Response time above 200ms');
} else {
pm.expect(pm.response.responseTime).to.be.below(201);
}
});

B. pm.test('Response time check', () => {
pm.expect(pm.response.responseTime).to.be.below(200);
if(pm.response.responseTime > 300) {
console.warn('Warning: Response time above 300ms');
}
});

C. pm.test('Response time check', () => {
if(pm.response.responseTime > 200) {
pm.expect.fail('Response time too high');
} else {
pm.expect(pm.response.responseTime).to.be.below(300);
}
});

D. pm.test('Response time check', () => {
pm.expect(pm.response.responseTime).to.be.below(300);
if(pm.response.responseTime > 200) {
pm.expect.fail('Response time warning');
}
});

Solution

1. Step 1: Understand the requirement

   Fail test if response time > 300ms, warn if > 200ms but ≤ 300ms, pass otherwise.

2. Step 2: Analyze each option logic

   pm.test('Response time check', () => { if(pm.response.responseTime > 300) { pm.expect.fail('Response time too high'); } else if(pm.response.responseTime > 200) { console.warn('Warning: Response time above 200ms'); } else { pm.expect(pm.response.responseTime).to.be.below(201); } }); correctly fails if > 300, warns if between 201 and 300, and passes if ≤ 200. Others either fail incorrectly or misuse warnings.

3. Final Answer:

   pm.test('Response time check', () => { if(pm.response.responseTime > 300) { pm.expect.fail('Response time too high'); } else if(pm.response.responseTime > 200) { console.warn('Warning: Response time above 200ms'); } else { pm.expect(pm.response.responseTime).to.be.below(201); } }); -> Option A

4. Quick Check:

   Fail above 300, warn above 200, else pass [OK]

Hint: Use if-else to separate fail, warn, and pass conditions [OK]

Common Mistakes:

• Failing test on warning condition
• Using console.warn without fail for errors
• Incorrect order of conditions causing wrong results