Response time benchmarking in Postman - Build an Automation Script

Benchmark API response time for GET /users endpoint

Preconditions (2)

Step 1: Open Postman and create a new GET request to https://api.example.com/users

Step 2: Send the request

Step 3: Record the response time shown in Postman

Step 4: Verify the response status code is 200

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

✅ Expected Result: The GET /users request returns status code 200 and the response time is under 500 milliseconds

Automation Requirements - Postman test scripts

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.response.responseTime for response time measurement

Write clear and concise test scripts inside the Tests tab

Avoid hardcoding URLs; use environment variables if possible

Automated Solution

Postman

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

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

The first test checks that the API returns a status code of 200, which means the request was successful.

The second test checks that the response time is less than 500 milliseconds, ensuring the API is fast enough.

Both tests use Postman's built-in pm object for assertions, which is the recommended way to write tests in Postman.

Common Mistakes - 3 Pitfalls

Checking response time using deprecated or incorrect properties

Not asserting the status code before checking response time

Hardcoding the API URL inside the test script

Bonus Challenge

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

Show Hint

Practice

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

easy

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

B. The size of the response body

C. The number of requests sent

D. The status code of the response

Solution

1. Step 1: Understand the purpose of pm.response.responseTime

   This property records how long the server takes to send back a response after a request is made.

2. Step 2: Differentiate from other response properties

   It does not measure response size, count requests, or check status codes; it only measures response speed.

3. Final Answer:

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

4. Quick Check:

   Response time = server speed [OK]

Hint: Response time means how fast server replies [OK]

Common Mistakes:

• Confusing response time with response size
• Thinking it counts requests instead of timing
• Mixing it up with status code checks

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

easy

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

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

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

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

Solution

1. Step 1: Identify correct assertion syntax in Postman

   Postman uses Chai assertion library syntax: pm.expect(value).to.be.below(limit) to check if value is less than limit.

2. Step 2: Check each option's logic and syntax

   pm.test('Response time is less than 500ms', () => pm.expect(pm.response.responseTime).to.be.below(500)); correctly uses pm.expect(pm.response.responseTime).to.be.below(500). pm.test('Response time is less than 500ms', () => pm.response.responseTime < 500); lacks assertion method. The version checking greater than 500 reverses the logic, and the version checking equality to 500 uses the wrong matcher.

3. Final Answer:

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

4. Quick Check:

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

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

Common Mistakes:

• Using comparison operators without pm.expect
• Checking for equality instead of less than
• Reversing comparison logic

3. Given 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 350 ms, what will be the test result?

medium

A. Test fails because 350 is not below 300

B. Test passes because 350 is below 300

C. Test passes because response time is ignored

D. Test throws a syntax error

Solution

1. Step 1: Understand the assertion condition

   The test expects response time to be less than 300 ms using to.be.below(300).

2. Step 2: Compare actual response time with expected limit

   The actual response time is 350 ms, which is greater than 300 ms, so the assertion fails.

3. Final Answer:

   Test fails because 350 is not below 300 -> Option A

4. Quick Check:

   350 > 300 means assertion fails [OK]

Hint: If actual > limit, test fails for 'to.be.below' [OK]

Common Mistakes:

• Thinking 350 is less than 300
• Assuming test passes without checking values
• Confusing syntax error with assertion failure

4. You wrote this Postman test to check response time:

pm.test('Response time under 200ms', () => {
  pm.expect(pm.response.responseTime).below(200);
});

But the test always passes even when response time is 500 ms. What is the error?

medium

A. Response time property is misspelled

B. Using pm.expect incorrectly without parentheses

C. Missing to.be before below(200)

D. Test name is incorrect

Solution

1. Step 1: Check assertion syntax correctness

   The correct Chai syntax requires chaining to.be.below(200). The code uses pm.expect(...).below(200) missing to.be.

2. Step 2: Understand effect of missing chain

   Without to.be, the assertion does not execute properly and silently passes, ignoring the actual response time.

3. Final Answer:

   Missing to.be before below(200) -> Option C

4. Quick Check:

   Use full chain pm.expect(...).to.be.below(...) [OK]

Hint: Always use pm.expect(...).to.be.below(...) chain [OK]

Common Mistakes:

• Omitting 'to.be' in assertion chain
• Misspelling responseTime property
• Ignoring test failure due to syntax

5. You want to benchmark response times for multiple API endpoints in Postman and fail the test if any response time exceeds 400 ms. Which approach is best?

hard

A. Write a test script in each request using pm.expect(pm.response.responseTime).to.be.below(400)

B. Use a collection-level test script that checks pm.response.responseTime after each request

C. Manually check response times in Postman console after running all requests

D. Set a global variable with response time and compare after all requests finish

Solution

1. Step 1: Understand scope of test scripts in Postman

   Collection-level scripts run after every request in the collection, allowing centralized checks for all endpoints.

2. Step 2: Compare options for efficiency and automation

   Use a collection-level test script that checks pm.response.responseTime after each request automates response time checks for all requests without repeating code. Writing a test script in each request using pm.expect(pm.response.responseTime).to.be.below(400) duplicates code, manually checking response times in Postman console after running all requests is error-prone, and setting a global variable with response time and comparing after all requests finish complicates logic unnecessarily.

3. Final Answer:

   Use a collection-level test script that checks pm.response.responseTime after each request -> Option B

4. Quick Check:

   Collection-level scripts automate checks for all requests [OK]

Hint: Use collection-level tests to check all response times automatically [OK]

Common Mistakes:

• Repeating same test in every request script
• Relying on manual checking instead of automation
• Overcomplicating with global variables