JSON value assertions in Postman - Test Execution Trace

Test Overview

This test sends a GET request to a sample API endpoint and verifies that the JSON response contains specific values. It checks that the user ID is 1 and the username is 'Bret'.

Test Code - Postman

Postman

pm.test("Verify JSON response values", () => {
    const jsonData = pm.response.json();
    pm.expect(jsonData.id).to.eql(1);
    pm.expect(jsonData.username).to.eql("Bret");
});

Execution Trace - 5 Steps

Step	Action	System State	Assertion	Result
1	Send GET request to https://jsonplaceholder.typicode.com/users/1	Request sent, waiting for response	—	PASS
2	Receive JSON response with user data	Response body contains JSON with fields including id and username	—	PASS
3	Parse JSON response to extract fields	jsonData object created with response values	—	PASS
4	Assert that jsonData.id equals 1	jsonData.id is 1	pm.expect(jsonData.id).to.eql(1)	PASS
5	Assert that jsonData.username equals 'Bret'	jsonData.username is 'Bret'	pm.expect(jsonData.username).to.eql("Bret")	PASS

Failure Scenario

Failing Condition: The JSON response contains a different user ID or username than expected

Execution Trace Quiz - 3 Questions

What does the test verify about the JSON response?

A That the JSON response is empty

B That the response status is 404

C That the user ID is 1 and username is 'Bret'

D That the user email is '[e-mail]'

Key Result

Always verify specific JSON values in API responses to ensure the API returns correct data, using clear and direct assertions.

Practice

1. What is the main purpose of JSON value assertions in Postman?

easy

A. To send requests to the server

B. To check if the API response data matches expected values

C. To format JSON data for display

D. To create new API endpoints

Solution

1. Step 1: Understand JSON value assertions

   JSON value assertions verify that the data returned by an API is correct and matches what is expected.

2. Step 2: Identify the purpose in Postman

   In Postman, assertions are used to check API responses, not to send requests or format data.

3. Final Answer:

   To check if the API response data matches expected values -> Option B

4. Quick Check:

   Assertions verify response data = A [OK]

Hint: Assertions check response data correctness fast [OK]

Common Mistakes:

• Confusing assertions with sending requests
• Thinking assertions format JSON
• Believing assertions create APIs

2. Which of the following is the correct syntax to assert that the JSON response 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. assert(pm.response.status == 'success');

Solution

1. Step 1: Identify correct assertion syntax in Postman

   Postman uses pm.expect() with the JSON response accessed by pm.response.json(). The method to check equality is .to.eql()

2. Step 2: Eliminate incorrect options

   pm.expect(pm.response.json().status).to.eql('success'); correctly uses pm.expect(pm.response.json().status).to.eql('success'); The other options have syntax errors or incorrect usage such as wrong response reference, missing pm.expect, or invalid functions.

3. Final Answer:

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

4. Quick Check:

   pm.expect + pm.response.json() + .to.eql() = D [OK]

Hint: Use pm.expect with pm.response.json() and .to.eql() [OK]

Common Mistakes:

• Using == instead of .to.eql()
• Missing pm.expect wrapper
• Referencing response incorrectly

3. Given the following Postman test code:

const jsonData = pm.response.json();
pm.expect(jsonData.user.id).to.eql(12345);

What will happen if the API response JSON is { "user": { "id": 12345, "name": "Alice" } }?

medium

A. The test will pass because the user id matches 12345

B. The test will fail because the user id is a number, not a string

C. The test will fail due to syntax error

D. The test will pass but ignore the user id

Solution

1. Step 1: Analyze the JSON response

   The response JSON has user.id equal to the number 12345, which matches the expected value in the assertion.

2. Step 2: Understand the assertion behavior

   pm.expect().to.eql() compares values strictly but 12345 number matches 12345 number, so the assertion passes.

3. Final Answer:

   The test will pass because the user id matches 12345 -> Option A

4. Quick Check:

   Matching values = test passes = B [OK]

Hint: Check exact value and type in JSON for assertion [OK]

Common Mistakes:

• Assuming number vs string mismatch causes failure
• Confusing syntax error with assertion failure
• Ignoring actual JSON structure

4. You wrote this Postman test:

pm.expect(pm.response.json().data).to.equal({"status": "active"});

But the test always fails even when the API returns { "data": { "status": "active" } }. What is the likely problem?

medium

A. The assertion should use .to.eql() for deep equality

B. The response JSON is not parsed correctly

C. Using .to.equal() instead of .to.eql() for object comparison

D. The test is missing pm.response.json() call

Solution

1. Step 1: Understand difference between .to.equal() and .to.eql()

   .to.equal() checks strict equality for primitives but can fail for objects or deep checks. .to.eql() is used for deep equality including strings and objects.

2. Step 2: Identify the correct assertion for object value

   Since 'data' is an object, .to.eql() is required for deep equality checks. Using .to.equal() performs strict reference equality (===), which fails for distinct object instances even if contents match.

3. Final Answer:

   The assertion should use .to.eql() for deep equality -> Option A

4. Quick Check:

   Use .to.eql() for object equality in JSON assertions [OK]

Hint: Use .to.eql() for JSON value assertions, not .to.equal() [OK]

Common Mistakes:

• Confusing .to.equal() and .to.eql()
• Assuming JSON parsing failed
• Missing pm.response.json() call

5. You want to assert that the API response JSON contains an array 'items' where each item has a 'price' greater than 0. Which Postman test code correctly checks this?

hard

A. pm.expect(pm.response.json().items.filter(price > 0)).to.not.be.empty;

B. pm.expect(pm.response.json().items).to.have.property('price').above(0);

C. pm.expect(pm.response.json().items.price).to.be.above(0);

D. pm.expect(pm.response.json().items.every(item => item.price > 0)).to.be.true;

Solution

1. Step 1: Understand the requirement

   We need to check that every item in the 'items' array has a 'price' greater than 0.

2. Step 2: Analyze each option

   pm.expect(pm.response.json().items.every(item => item.price > 0)).to.be.true; uses JavaScript's every() method to check all items satisfy price > 0, then asserts true. This is correct.
   pm.expect(pm.response.json().items).to.have.property('price').above(0); incorrectly tries to check property on array directly.
   pm.expect(pm.response.json().items.price).to.be.above(0); tries to access items.price which is invalid since items is an array.
   pm.expect(pm.response.json().items.filter(price > 0)).to.not.be.empty; uses filter incorrectly without a function.

3. Final Answer:

   pm.expect(pm.response.json().items.every(item => item.price > 0)).to.be.true; -> Option D

4. Quick Check:

   Use every() with pm.expect to check all array items [OK]

Hint: Use .every() to assert all array items meet condition [OK]

Common Mistakes:

• Trying to access property on array directly
• Using filter without a function
• Misusing assertion methods on arrays