Response body assertions in Postman - Build an Automation Script

Verify response body contains expected user data

Preconditions (2)

Step 1: Send a GET request to https://api.example.com/users/123

Step 2: Check the response status code is 200

Step 3: Verify the response body contains a JSON object with keys: id, name, email

Step 4: Verify the id value is 123

Step 5: Verify the name value is 'John Doe'

Step 6: Verify the email value is '[e-mail]'

✅ Expected Result: Response status code is 200 and response body JSON contains correct user data as specified

Automation Requirements - Postman Tests

Assertions Needed:

Status code is 200

Response body has keys: id, name, email

id equals 123

name equals 'John Doe'

email equals '[e-mail]'

Best Practices:

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

Use pm.response.json() to parse response body

Use strict equality checks for values

Write clear and descriptive assertion messages

Automated Solution

Postman

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

pm.test('Response body has expected user data', () => {
    const jsonData = pm.response.json();
    pm.expect(jsonData).to.have.all.keys('id', 'name', 'email');
    pm.expect(jsonData.id).to.eql(123);
    pm.expect(jsonData.name).to.eql('John Doe');
    pm.expect(jsonData.email).to.eql('[e-mail]');
});

The first test checks that the response status code is exactly 200 using pm.response.to.have.status(200). This ensures the request was successful.

The second test parses the response body JSON with pm.response.json(). It then asserts the JSON object has all the keys id, name, and email using to.have.all.keys. This confirms the expected data structure.

Finally, it checks each key's value matches the expected data using strict equality to.eql(). This verifies the correctness of the response content.

Each assertion has a clear message to help identify failures during test runs.

Common Mistakes - 4 Pitfalls

Not checking the status code before validating response body

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

Not parsing the response body JSON before accessing keys

Hardcoding values without verifying the response structure first

Bonus Challenge

Now add data-driven testing with 3 different user IDs and expected user data

Show Hint

Practice

1. What does pm.response.json() do in Postman tests?

easy

A. It parses the response body as a JSON object.

B. It sends a new request to the server.

C. It clears the response body.

D. It validates the response status code.

Solution

1. Step 1: Understand the purpose of pm.response.json()

   This function reads the response body and converts it into a JSON object for easy access.

2. Step 2: Compare with other options

   Sending requests, clearing body, or validating status are different functions, not pm.response.json().

3. Final Answer:

   It parses the response body as a JSON object. -> Option A

4. Quick Check:

   Parsing response body = A [OK]

Hint: Remember: json() reads response body as JSON [OK]

Common Mistakes:

• Confusing json() with sending requests
• Thinking json() clears data
• Mixing response body parsing with status code checks

2. Which of the following is the correct syntax to assert that the response JSON has a key status with value success in Postman?

easy

A. pm.expect(response.status).to.equal('success');

B. pm.response.json().status == 'success';

C. pm.expect(pm.response.json().status).to.eql('success');

D. pm.assert(pm.response.status == 'success');

Solution

1. Step 1: Identify correct assertion syntax in Postman

   Postman uses pm.expect() with Chai assertion style, so pm.expect(pm.response.json().status).to.eql('success'); is correct.

2. Step 2: Check other options for errors

   pm.response.json().status == 'success'; lacks assertion, C uses wrong object, D uses incorrect method.

3. Final Answer:

   pm.expect(pm.response.json().status).to.eql('success'); -> Option C

4. Quick Check:

   Use pm.expect() with to.eql() for value check [OK]

Hint: Use pm.expect() with to.eql() for JSON value checks [OK]

Common Mistakes:

• Using == instead of pm.expect() for assertions
• Referencing response.status instead of response.json().status
• Using pm.assert() which is not a Postman function

3. Given this response body:

{"user":{"id":5,"name":"Alice"}}

What will this test output?

const jsonData = pm.response.json();
pm.test("User ID is 5", () => {
  pm.expect(jsonData.user.id).to.equal(5);
});

medium

A. Test passes because user.id equals 5.

B. Test fails because user.id is not 5.

C. Test throws an error due to syntax.

D. Test is skipped because no assertion is made.

Solution

1. Step 1: Parse the response JSON

   The response has user.id = 5, so jsonData.user.id is 5.

2. Step 2: Evaluate the assertion

   The test asserts jsonData.user.id equals 5, which is true, so the test passes.

3. Final Answer:

   Test passes because user.id equals 5. -> Option A

4. Quick Check:

   Value matches assertion = Pass [OK]

Hint: Match JSON path value with expected to pass test [OK]

Common Mistakes:

• Misreading JSON structure
• Assuming test fails without checking value
• Confusing syntax errors with assertion failures

4. Identify the error in this Postman test code:

const data = pm.response.json();
pm.test("Check user name", () => {
  pm.expect(data.user.name).to.equal('Bob')
});

medium

A. Missing semicolon after assertion line.

B. No error; the test code is correct.

C. Incorrect function name; should be pm.test, not pm.tests.

D. Missing parentheses after pm.expect.

Solution

1. Step 1: Review syntax of Postman test code

   The code uses pm.test correctly, with proper arrow function and assertion syntax.

2. Step 2: Check for syntax errors

   Semicolons are optional in JavaScript; parentheses and function names are correct.

3. Final Answer:

   No error; the test code is correct. -> Option B

4. Quick Check:

   Correct syntax means no error [OK]

Hint: Check function names and parentheses carefully [OK]

Common Mistakes:

• Confusing pm.test with pm.tests
• Thinking semicolons are mandatory
• Missing parentheses in pm.expect

5. You want to assert that the response JSON array items contains an object with id equal to 10. Which test code correctly checks this in Postman?

hard

A. pm.expect(pm.response.json().items.id).to.equal(10);

B. const items = pm.response.json().items;
pm.expect(items.find(id => id === 10)).to.exist;

C. pm.expect(pm.response.json().items.includes({id:10})).to.be.true;

D. const items = pm.response.json().items;
pm.expect(items.some(item => item.id === 10)).to.be.true;

Solution

1. Step 1: Understand the response structure

   items is an array of objects; we want to check if any object has id 10.

2. Step 2: Evaluate each option

   const items = pm.response.json().items; pm.expect(items.some(item => item.id === 10)).to.be.true; uses some() to check if any item has id === 10, which is correct. pm.expect(pm.response.json().items.id).to.equal(10); wrongly accesses items.id (invalid). pm.expect(pm.response.json().items.includes({id:10})).to.be.true; tries to use includes() with an object, which won't work. const items = pm.response.json().items; pm.expect(items.find(id => id === 10)).to.exist; uses find() but the callback is incorrect (should check item.id).

3. Final Answer:

   const items = pm.response.json().items; pm.expect(items.some(item => item.id === 10)).to.be.true; -> Option D

4. Quick Check:

   Use some() with correct callback for array check [OK]

Hint: Use some() to check if array contains object with property [OK]

Common Mistakes:

• Using includes() with objects (doesn't work)
• Accessing array properties directly
• Incorrect callback function in find()