JSON value assertions in Postman - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ assertion

intermediate

Check if JSON response contains a specific key with expected value

Given the JSON response below, which Postman test script assertion correctly verifies that the user's status is 'active'?

Postman

{
  "user": {
    "id": 101,
    "name": "Alice",
    "status": "active"
  }
}

A pm.test('User status is active', () => { pm.expect(pm.response.json().user.status).to.eql('active'); });

B pm.test('User status is active', () => { pm.expect(pm.response.json().user.status).to.equal('inactive'); });

C pm.test('User status is active', () => { pm.expect(pm.response.json().status).to.eql('active'); });

D pm.test('User status is active', () => { pm.expect(pm.response.json().user.status).to.be.true; });

💡 Hint

Look carefully at the JSON structure and the expected value in the assertion.

Option A correctly accesses the nested 'status' key inside 'user' and checks if it equals 'active'. Option A checks for 'inactive' which is wrong. Option A tries to access 'status' at the root level, which does not exist. Option A incorrectly expects a boolean value.

❓ assertion

intermediate

Verify array length in JSON response

Which Postman test script assertion correctly verifies that the 'items' array in the JSON response has exactly 3 elements?

Postman

{
  "items": ["apple", "banana", "cherry"]
}

A pm.test('Items array length is 3', () => { pm.expect(pm.response.json().items).to.have.lengthOf(4); });

B pm.test('Items array length is 3', () => { pm.expect(pm.response.json().items.length).to.eql(3); });

C pm.test('Items array length is 3', () => { pm.expect(pm.response.json().items.length).to.equal('3'); });

D pm.test('Items array length is 3', () => { pm.expect(pm.response.json().items).to.be.an('object'); });

💡 Hint

Check the length property and the expected number type.

Option B correctly checks that the length of the 'items' array is 3. Option B checks for length 4 which is incorrect. Option B compares length to string '3' instead of number 3, causing a failed assertion. Option B wrongly expects 'items' to be an object instead of an array.

❓ Predict Output

advanced

Output of JSON value assertion with nested arrays

What will be the result of this Postman test script when run against the given JSON response?

Postman

const jsonData = pm.response.json();
pm.test('Check second tag is "urgent"', () => {
  pm.expect(jsonData.tags[1]).to.eql('urgent');
});

A Test throws an error because 'tags' is not an array.

B Test fails because the second tag is 'important'.

C Test fails because the second tag is undefined.

D Test passes because the second tag is 'urgent'.

💡 Hint

Look at the JSON response structure and the value at index 1 in the 'tags' array.

The JSON response has 'tags' as ["normal", "urgent", "review"]. The second element (index 1) is 'urgent', so the assertion passes.

🔧 Debug

advanced

Identify the error in JSON value assertion

This Postman test script is intended to check if the 'price' in the JSON response is 19.99. What error will occur when running this script?

Postman

pm.test('Price is 19.99', () => {
  pm.expect(pm.response.json().price).to.equal(19.99);
});

A TypeError because 'price' is undefined in the JSON response.

B AssertionError because the price is 20.00, not 19.99.

C SyntaxError due to missing parentheses.

D No error; test passes successfully.

💡 Hint

Check if the JSON response contains the 'price' key.

If the JSON response does not have a 'price' key, accessing pm.response.json().price returns undefined. Then the assertion tries to compare undefined to 19.99, causing a TypeError.

🧠 Conceptual

expert

Best practice for asserting optional JSON keys in Postman

In a JSON response, some keys may or may not be present. Which Postman test script snippet correctly asserts that if the key 'discount' exists, its value must be greater than 0, but does not fail if 'discount' is missing?

A pm.test('Discount check', () => { if (pm.response.json().discount) { pm.expect(pm.response.json().discount).to.be.above(0); } });

B pm.test('Discount check', () => { pm.expect(pm.response.json().discount).to.be.above(0); });

C pm.test('Discount check', () => { const d = pm.response.json().discount; if (d !== undefined) { pm.expect(d).to.be.above(0); } });

D pm.test('Discount check', () => { pm.expect(pm.response.json().discount).to.exist.and.to.be.above(0); });

💡 Hint

Consider how to avoid errors when the key is missing.

Option C safely checks if 'discount' exists before asserting its value. Option C fails if 'discount' is missing (undefined). Option C tries to chain 'to.exist' and 'to.be.above(0)' which causes an error if 'discount' is undefined. Option C fails if 'discount' is 0 because 0 is falsy, so the check is skipped incorrectly.