Extracting data from responses in Postman - Build an Automation Script

Extract user ID from API response and verify it

Preconditions (2)

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

Step 2: Wait for the response

Step 3: Extract the 'id' field from the JSON response body

Step 4: Verify that the extracted 'id' equals 123

✅ Expected Result: The 'id' field is extracted successfully and equals 123

Automation Requirements - Postman Tests (JavaScript)

Assertions Needed:

Verify response status code is 200

Verify extracted 'id' field equals 123

Best Practices:

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

Use pm.test() for assertions

Use descriptive test names

Avoid hardcoding values except for verification

Automated Solution

Postman

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

const responseJson = pm.response.json();
const userId = responseJson.id;

pm.test('User ID is 123', () => {
    pm.expect(userId).to.eql(123);
});

The first test checks that the response status code is 200, which means the request was successful.

Then, we parse the JSON response using pm.response.json() to get a JavaScript object.

We extract the id field from the response object and store it in userId.

Finally, we assert that userId equals 123 using pm.expect().to.eql(). This confirms the correct data was returned.

Common Mistakes - 3 Pitfalls

Not parsing the response JSON before accessing fields

Using incorrect assertion syntax like pm.expect(userId == 123)

Not checking response status before extracting data

Bonus Challenge

Now add tests to extract and verify 'username' and 'email' fields from the response

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