Response headers in Postman - Build an Automation Script

Verify response headers for a GET request

Preconditions (2)

Step 1: Open Postman

Step 2: Create a new GET request to https://api.example.com/data

Step 3: Send the request

Step 4: Check the response headers section

✅ Expected Result: The response headers include 'Content-Type' with value 'application/json' and 'Cache-Control' with value 'no-cache'

Automation Requirements - Postman test scripts

Assertions Needed:

Verify 'Content-Type' header exists and equals 'application/json'

Verify 'Cache-Control' header exists and equals 'no-cache'

Best Practices:

Use pm.response.headers.get() to access headers

Use strict equality checks for header values

Write clear and descriptive assertion messages

Automated Solution

Postman

pm.test('Content-Type header is application/json', () => {
    const contentType = pm.response.headers.get('Content-Type');
    pm.expect(contentType).to.eql('application/json');
});

pm.test('Cache-Control header is no-cache', () => {
    const cacheControl = pm.response.headers.get('Cache-Control');
    pm.expect(cacheControl).to.eql('no-cache');
});

The first test checks if the 'Content-Type' header is exactly 'application/json'. We use pm.response.headers.get() to get the header value and pm.expect().to.eql() for strict equality.

The second test does the same for the 'Cache-Control' header, verifying it equals 'no-cache'.

This approach ensures the headers are present and have the expected values, which is important for API correctness.

Common Mistakes - 3 Pitfalls

{'mistake': "Using pm.response.headers['Content-Type'] instead of pm.response.headers.get()", 'why_bad': 'pm.response.headers is not a plain object, so direct property access returns undefined.', 'correct_approach': "Use pm.response.headers.get('Content-Type') to correctly retrieve header values."}

Using loose equality (==) instead of strict equality (=== or to.eql()) in assertions

Not checking if the header exists before asserting its value

Bonus Challenge

Now add data-driven testing with 3 different API endpoints and verify their 'Content-Type' headers

Show Hint

Practice

1. What does the pm.response.headers.get('Content-Type') command do in Postman tests?

easy

A. It lists all headers in the response.

B. It sets the 'Content-Type' header in the request.

C. It deletes the 'Content-Type' header from the response.

D. It retrieves the value of the 'Content-Type' header from the response.

Solution

1. Step 1: Understand the method purpose

   The method pm.response.headers.get() is used to read a specific header from the response.

2. Step 2: Apply to 'Content-Type' header

   Using 'Content-Type' as the argument returns the value of that header from the server's reply.

3. Final Answer:

   It retrieves the value of the 'Content-Type' header from the response. -> Option D

4. Quick Check:

   pm.response.headers.get('Content-Type') = header value [OK]

Hint: Get header value with pm.response.headers.get('Header-Name') [OK]

Common Mistakes:

• Confusing get() with setting headers
• Thinking it deletes headers
• Assuming it returns all headers

2. Which of the following is the correct syntax to check if the response header 'Cache-Control' equals 'no-cache' in a Postman test script?

easy

A. pm.response.headers.get('Cache-Control') === 'no-cache';

B. pm.response.headers['Cache-Control'] == 'no-cache';

C. pm.response.headers.get('Cache-Control') = 'no-cache';

D. pm.response.headers.has('Cache-Control', 'no-cache');

Solution

1. Step 1: Identify correct method to get header value

   The method to get a header value is pm.response.headers.get('Header-Name').

2. Step 2: Use strict equality to compare value

   To check if the header equals 'no-cache', use === 'no-cache' for exact match.

3. Final Answer:

   pm.response.headers.get('Cache-Control') === 'no-cache'; -> Option A

4. Quick Check:

   Use get() + === for header value check [OK]

Hint: Use get() and === to compare header values correctly [OK]

Common Mistakes:

• Using single = instead of === for comparison
• Trying to access headers like an object property
• Using non-existent has() method with two arguments

3. Given this Postman test code:

const server = pm.response.headers.get('Server');
pm.test('Server header is Apache', () => {
  pm.expect(server).to.equal('Apache');
});

What will happen if the response header 'Server' is actually 'nginx'?

medium

A. The test will fail because the header value is not 'Apache'.

B. The test will be skipped automatically.

C. The test will throw a syntax error.

D. The test will pass because the header exists.

Solution

1. Step 1: Understand the test expectation

   The test expects the 'Server' header value to be exactly 'Apache'.

2. Step 2: Compare actual header value

   If the actual header is 'nginx', the expectation pm.expect(server).to.equal('Apache') will fail.

3. Final Answer:

   The test will fail because the header value is not 'Apache'. -> Option A

4. Quick Check:

   Expected 'Apache', got 'nginx' = fail [OK]

Hint: Test fails if header value differs from expected string [OK]

Common Mistakes:

• Assuming test passes if header exists
• Confusing syntax error with assertion failure
• Thinking test skips on mismatch

4. You wrote this Postman test to check the 'Content-Length' header:

pm.test('Content-Length is 1234', () => {
  pm.expect(pm.response.headers.get('Content-Length')).to.equal(1234);
});

But the test always fails even when the header shows '1234'. What is the likely problem?

medium

A. pm.response.headers.get() cannot read 'Content-Length'.

B. The header name is case-sensitive and should be lowercase.

C. The header value is a string, but test compares to a number.

D. The test syntax is invalid and causes an error.

Solution

1. Step 1: Check data types in comparison

   The header value returned by pm.response.headers.get() is always a string.

2. Step 2: Identify mismatch in expected value type

   The test compares the string '1234' to the number 1234, causing the equality check to fail.

3. Final Answer:

   The header value is a string, but test compares to a number. -> Option C

4. Quick Check:

   Compare string to string to pass test [OK]

Hint: Compare header values as strings, not numbers [OK]

Common Mistakes:

• Comparing string header to number directly
• Assuming header names are case-sensitive
• Believing get() cannot read standard headers

5. You want to write a Postman test that fails if the response does NOT include the header X-Security or if its value is not enabled. Which code snippet correctly implements this?

hard

A. pm.test('X-Security header check', () => {
const header = pm.response.headers.get('X-Security');
pm.expect(header || 'enabled').to.equal('enabled');
});

B. pm.test('X-Security header check', () => {
pm.expect(pm.response.headers.has('X-Security')).to.be.true;
pm.expect(pm.response.headers.get('X-Security')).to.equal('enabled');
});

C. pm.test('X-Security header check', () => {
pm.expect(pm.response.headers.get('X-Security')).to.be.true;
pm.expect(pm.response.headers.get('X-Security')).to.equal('enabled');
});

D. pm.test('X-Security header check', () => {
pm.expect(pm.response.headers.has('X-Security', 'enabled')).to.be.true;
});

Solution

1. Step 1: Check header existence explicitly

   Use pm.response.headers.has('X-Security') to confirm the header is present.

2. Step 2: Verify header value equals 'enabled'

   Use pm.response.headers.get('X-Security') and compare with 'enabled' using to.equal().

3. Step 3: Combine both checks in one test

   Both conditions must be true for the test to pass, ensuring header presence and correct value.

4. Final Answer:

   Use has() to check presence and get() to check value. -> Option B

5. Quick Check:

   has() + get() ensures header exists and matches value [OK]

Hint: Use has() to check header exists before checking value [OK]

Common Mistakes:

• Not checking header existence before value
• Using get() without verifying header presence
• Assuming get() returns undefined if header missing