Nested object assertions in Postman - Build an Automation Script

Verify nested object values in API response

Preconditions (2)

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

Step 2: Check the response status code is 200

Step 3: Verify the response body contains a 'user' object

Step 4: Inside 'user', verify 'id' equals 123

Step 5: Inside 'user', verify 'profile' object exists

Step 6: Inside 'profile', verify 'name' equals 'John Doe'

Step 7: Inside 'profile', verify 'address' object exists

Step 8: Inside 'address', verify 'city' equals 'New York'

Step 9: Inside 'address', verify 'zip' equals '10001'

✅ Expected Result: The API response status is 200 and all nested object values match the expected data.

Automation Requirements - Postman test scripts (JavaScript)

Assertions Needed:

Status code is 200

'user' object exists

'user.id' equals 123

'user.profile' object exists

'user.profile.name' equals 'John Doe'

'user.profile.address' object exists

'user.profile.address.city' equals 'New York'

'user.profile.address.zip' equals '10001'

Best Practices:

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

Use pm.expect with deep property access for nested assertions

Check object existence before accessing nested properties

Write clear and descriptive assertion messages

Automated Solution

Postman

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

const jsonData = pm.response.json();

pm.test('Response has user object', () => {
    pm.expect(jsonData).to.have.property('user');
});

pm.test('User id is 123', () => {
    pm.expect(jsonData.user).to.have.property('id', 123);
});

pm.test('User profile object exists', () => {
    pm.expect(jsonData.user).to.have.property('profile');
});

pm.test('User profile name is John Doe', () => {
    pm.expect(jsonData.user.profile).to.have.property('name', 'John Doe');
});

pm.test('User profile address object exists', () => {
    pm.expect(jsonData.user.profile).to.have.property('address');
});

pm.test('User profile address city is New York', () => {
    pm.expect(jsonData.user.profile.address).to.have.property('city', 'New York');
});

pm.test('User profile address zip is 10001', () => {
    pm.expect(jsonData.user.profile.address).to.have.property('zip', '10001');
});

This script uses Postman test scripts written in JavaScript to automate the manual test case.

First, it checks the HTTP status code is 200 using pm.response.to.have.status(200).

Then, it parses the JSON response body with pm.response.json() and stores it in jsonData.

Each pm.test block verifies a specific nested property. It first checks if the parent object exists before accessing child properties to avoid errors.

Assertions use pm.expect(...).to.have.property(...) to check both existence and exact values.

This approach ensures clear, step-by-step validation of nested objects, making debugging easier if a test fails.

Common Mistakes - 3 Pitfalls

Accessing nested properties without checking if parent objects exist

{'mistake': 'Using incorrect assertion syntax like pm.expect(jsonData.user.id == 123)', 'why_bad': 'This does not use the assertion library properly and may not fail the test correctly.', 'correct_approach': "Use pm.expect(jsonData.user).to.have.property('id', 123) for clear and reliable assertions."}

Not verifying the response status code before checking body content

Bonus Challenge

Now add data-driven testing with 3 different user IDs: 123, 456, and 789, verifying their respective nested profile data.

Show Hint

Practice

1. In Postman, how do you access a nested property user.name in a JSON response for assertion?

easy

A. Use pm.expect(jsonData.user[name]) to access nested property.

B. Use pm.expect(jsonData.user.name) to assert the nested value.

C. Use pm.expect(jsonData['user-name']) to access nested property.

D. Use pm.expect(jsonData.user-name) to access nested property.

Solution

1. Step 1: Understand JSON nested property access

   In JavaScript, nested properties are accessed using dot notation like object.property.

2. Step 2: Apply correct syntax in Postman test

   To assert user.name, use pm.expect(jsonData.user.name) which correctly accesses the nested value.

3. Final Answer:

   Use pm.expect(jsonData.user.name) to assert the nested value. -> Option B

4. Quick Check:

   Dot notation = pm.expect(jsonData.user.name) [OK]

Hint: Use dot notation for nested JSON properties in assertions [OK]

Common Mistakes:

• Using brackets incorrectly for nested keys
• Using hyphens instead of dots for nested access
• Missing quotes around string keys in bracket notation

2. Which of the following is the correct syntax to assert that response.body.data.user.age equals 30 in Postman?

easy

A. pm.test('Age is 30', () => { pm.expect(response.body.data.user.age).to.eql(30); });

B. pm.test('Age is 30', () => { pm.expect(response.body.data.user.age).to.equal('30'); });

C. pm.test('Age is 30', () => { pm.expect(response.body.data.user.age).to.be('30'); });

D. pm.test('Age is 30', () => { pm.expect(response.body.data.user.age).equals(30); });

Solution

1. Step 1: Identify correct assertion method

   Postman uses Chai assertion library where to.eql(value) checks deep equality including numbers.

2. Step 2: Check syntax correctness

   pm.test('Age is 30', () => { pm.expect(response.body.data.user.age).to.eql(30); }); uses to.eql(30) with correct arrow function and property access, matching expected number type.

3. Final Answer:

   pm.test('Age is 30', () => { pm.expect(response.body.data.user.age).to.eql(30); }); -> Option A

4. Quick Check:

   Use to.eql for value equality in Postman tests [OK]

Hint: Use to.eql() for exact value matching in Postman assertions [OK]

Common Mistakes:

• Using string '30' instead of number 30
• Using incorrect assertion methods like to.be()
• Missing arrow function syntax in pm.test

3. Given the JSON response:

{"order": {"id": 101, "items": [{"name": "Pen", "qty": 3}, {"name": "Book", "qty": 2}]}}

What will this Postman test output?

pm.test('Check first item qty', () => {
  const jsonData = pm.response.json();
  pm.expect(jsonData.order.items[0].qty).to.eql(3);
});

medium

A. Test will pass because first item's qty is 3.

B. Test will fail because qty is 2 for first item.

C. Test will throw an error due to wrong index access.

D. Test will fail because items is not an array.

Solution

1. Step 1: Analyze JSON structure and access

   The JSON has an array items with first element having qty: 3.

2. Step 2: Check assertion correctness

   The test accesses items[0].qty and asserts it equals 3, which matches the JSON data.

3. Final Answer:

   Test will pass because first item's qty is 3. -> Option A

4. Quick Check:

   Array index 0 qty = 3 matches assertion [OK]

Hint: Check array index and property value carefully in nested assertions [OK]

Common Mistakes:

• Confusing array index starting at 1 instead of 0
• Assuming items is an object, not an array
• Misreading qty values in nested objects

4. You wrote this Postman test:

pm.test('Check user city', () => {
  const jsonData = pm.response.json();
  pm.expect(jsonData.user.address.city).to.eql('New York');
});

But the test fails with error: TypeError: Cannot read property 'city' of undefined. What is the likely cause?

medium

A. The assertion method to.eql is incorrect for strings.

B. The city value is misspelled in the assertion.

C. The JSON response is not parsed correctly with pm.response.json().

D. The address property is missing or undefined in user.

Solution

1. Step 1: Understand the error message

   The error says Cannot read property 'city' of undefined, meaning address is undefined.

2. Step 2: Identify cause in nested access

   If jsonData.user.address is missing, trying to access .city causes this error.

3. Final Answer:

   The address property is missing or undefined in user. -> Option D

4. Quick Check:

   Undefined parent property causes TypeError in nested access [OK]

Hint: Check if all parent nested objects exist before accessing child [OK]

Common Mistakes:

• Assuming all nested keys always exist
• Ignoring error message details
• Blaming assertion method instead of data structure

5. You receive this JSON response:

{"users": [{"id": 1, "profile": {"name": "Alice", "active": true}}, {"id": 2, "profile": {"name": "Bob", "active": false}}]}

Write a Postman test to assert that all users have a profile.active property set to true. Which code snippet correctly performs this nested object assertion?

hard

A. pm.test('All users active', () => {
const users = pm.response.json().users;
pm.expect(users[0].every(user => user.profile.active)).to.eql(true);
});

B. pm.test('All users active', () => {
const users = pm.response.json().users;
pm.expect(users.profile.active).to.eql(true);
});

C. pm.test('All users active', () => {
const users = pm.response.json().users;
users.forEach(user => {
pm.expect(user.profile.active).to.eql(true);
});
});

D. pm.test('All users active', () => {
const users = pm.response.json().users;
users.map(user => pm.expect(user.profile).to.eql(true));
});

Solution

1. Step 1: Understand requirement to check all users' active status

   We must assert each user's profile.active is true.

2. Step 2: Evaluate each option's approach

   pm.test('All users active', () => { const users = pm.response.json().users; users.forEach(user => { pm.expect(user.profile.active).to.eql(true); }); }); loops over users and asserts each profile.active equals true, which is correct and clear.
   pm.test('All users active', () => { const users = pm.response.json().users; pm.expect(users.profile.active).to.eql(true); }); wrongly tries to access users.profile.active which is invalid.
   pm.test('All users active', () => { const users = pm.response.json().users; pm.expect(users[0].every(user => user.profile.active)).to.eql(true); }); wrongly calls every() on users[0] (an object), causing TypeError as objects have no every method.
   pm.test('All users active', () => { const users = pm.response.json().users; users.map(user => pm.expect(user.profile).to.eql(true)); }); asserts user.profile equals true, but profile is an object not equal to true and misses .active.

3. Final Answer:

   Use forEach loop to assert each user's profile.active is true. -> Option C

4. Quick Check:

   Loop and assert each nested property for all items [OK]

Hint: Use forEach to assert nested properties on all array items [OK]

Common Mistakes:

• Accessing nested property on array directly
• Calling array methods like every() on single objects
• Asserting entire object equals true instead of its boolean property