Extracting data from responses in Postman - Test Execution Trace

Test Overview

This test sends a GET request to a sample API endpoint and extracts a specific value from the JSON response. It verifies that the extracted value matches the expected result.

Test Code - Postman

Postman

pm.test("Extract user ID from response", function () {
    pm.sendRequest('https://jsonplaceholder.typicode.com/users/1', function (err, res) {
        pm.expect(err).to.be.null;
        pm.expect(res).to.have.property('status', 200);
        const jsonData = res.json();
        const userId = jsonData.id;
        pm.expect(userId).to.eql(1);
        pm.environment.set('extractedUserId', userId);
    });
});

Execution Trace - 5 Steps

Step	Action	System State	Assertion	Result
1	Test starts and sends GET request to 'https://jsonplaceholder.typicode.com/users/1'	Postman sends HTTP GET request to the API endpoint	—	PASS
2	Receives HTTP response with status code 200 and JSON body	Response contains user data JSON with id, name, username, etc.	Check that response status code is 200	PASS
3	Parses JSON response and extracts 'id' field value	Extracted userId = 1	Verify extracted userId equals 1	PASS
4	Stores extracted userId in environment variable 'extractedUserId'	Environment variable 'extractedUserId' set to 1	—	PASS
5	Test completes successfully	Test result marked as passed in Postman test runner	—	PASS

Failure Scenario

Failing Condition: Response status code is not 200 or 'id' field is missing or incorrect

Execution Trace Quiz - 3 Questions

What does the test verify after receiving the response?

A That the response body is empty

B That the request method is POST

C That the response status code is 200 and 'id' equals 1

D That the environment variable is deleted

Key Result

Always verify the response status code before extracting data, and store extracted values in environment variables for reuse in subsequent requests.

Practice

1. What is the primary purpose of extracting data from API responses in Postman?

easy

A. To reuse data in subsequent API requests

B. To change the API endpoint URL

C. To modify the request headers

D. To delete the response data

Solution

1. Step 1: Understand the role of data extraction

   Extracting data allows you to capture values from one response to use later.

2. Step 2: Connect API requests using extracted data

   This helps chain requests by passing data like tokens or IDs forward.

3. Final Answer:

   To reuse data in subsequent API requests -> Option A

4. Quick Check:

   Extract data = reuse in next requests [OK]

Hint: Extract data to pass info between requests [OK]

Common Mistakes:

• Thinking extraction changes the URL
• Confusing extraction with header modification
• Believing extraction deletes data

2. Which Postman script correctly extracts the value of userId from a JSON response and saves it as an environment variable?

easy

A. let data = pm.response.json(); pm.environment.set('userId', data.userId);

B. pm.response.set('userId', pm.response.json().userId);

C. pm.environment.get('userId', pm.response.json().userId);

D. let userId = pm.response.set('userId');

Solution

1. Step 1: Use pm.response.json() to parse JSON

   This method converts the response body into a JavaScript object.

2. Step 2: Use pm.environment.set() to save variable

   Set the environment variable 'userId' with the extracted value.

3. Final Answer:

   let data = pm.response.json(); pm.environment.set('userId', data.userId); -> Option A

4. Quick Check:

   Parse JSON + set env variable = let data = pm.response.json(); pm.environment.set('userId', data.userId); [OK]

Hint: Use pm.response.json() then pm.environment.set() [OK]

Common Mistakes:

• Using pm.response.set() which doesn't exist
• Using pm.environment.get() to set variables
• Not parsing JSON before accessing properties

3. Given the response body:

{"token": "abc123", "user": {"id": 42}}

What will this Postman script save in the environment variable authToken?

let jsonData = pm.response.json();
pm.environment.set('authToken', jsonData.token);

medium

A. null

B. 42

C. undefined

D. "abc123"

Solution

1. Step 1: Parse the JSON response

   jsonData.token accesses the 'token' key which has value "abc123".

2. Step 2: Set environment variable with token value

   pm.environment.set saves "abc123" as 'authToken'.

3. Final Answer:

   "abc123" -> Option D

4. Quick Check:

   jsonData.token = "abc123" [OK]

Hint: Access exact key from parsed JSON to get value [OK]

Common Mistakes:

• Using user.id instead of token
• Expecting number 42 instead of string token
• Not parsing JSON before accessing token

4. You wrote this Postman test script to extract sessionId from the response:

let data = pm.response.json();
pm.environment.set('sessionId', data.session_id);

But the environment variable sessionId is always empty. What is the likely problem?

medium

A. pm.response.json() does not parse JSON

B. pm.environment.set() cannot save variables

C. The response JSON uses sessionId not session_id

D. You must use pm.collectionVariables.set() instead

Solution

1. Step 1: Check JSON key names carefully

   The script uses 'session_id' but the response likely has 'sessionId' (camelCase).

2. Step 2: Correct key name to match response

   Use data.sessionId to correctly extract the value.

3. Final Answer:

   The response JSON uses sessionId not session_id -> Option C

4. Quick Check:

   Key name mismatch causes empty variable [OK]

Hint: Match JSON keys exactly, including case [OK]

Common Mistakes:

• Assuming pm.environment.set() doesn't work
• Not parsing JSON before accessing keys
• Confusing environment and collection variables

5. You receive this nested JSON response:

{"data": {"users": [{"id": 1, "name": "Alice"}, {"id": 2, "name": "Bob"}]}}

How do you extract and save the name of the second user as a collection variable in Postman?

hard

A. pm.environment.set('secondUserName', pm.response.json().data.users[1].name);

B. let json = pm.response.json(); pm.collectionVariables.set('secondUserName', json.data.users[1].name);

C. let json = pm.response.json(); pm.environment.set('secondUserName', json.data.users[2].name);

D. pm.collectionVariables.set('secondUserName', pm.response.json().users[2].name);

Solution

1. Step 1: Parse the nested JSON response

   Access the array at json.data.users and select index 1 for the second user.

2. Step 2: Save the second user's name as a collection variable

   Use pm.collectionVariables.set with key 'secondUserName' and value json.data.users[1].name.

3. Final Answer:

   let json = pm.response.json(); pm.collectionVariables.set('secondUserName', json.data.users[1].name); -> Option B

4. Quick Check:

   Index 1 in users array = second user name [OK]

Hint: Use zero-based index and correct variable scope [OK]

Common Mistakes:

• Using index 2 instead of 1 for second user
• Mixing environment and collection variables
• Not parsing JSON before accessing nested data