Test utilities and helpers in Postman - Build an Automation Script

Verify custom test utility function for response validation

Preconditions (2)

Step 1: Create a new Postman request with GET method to https://api.example.com/users

Step 2: Write a test utility function in the Tests tab that checks if the response status is 200

Step 3: Write a helper function that verifies the response body contains a 'users' array

Step 4: Call these utility and helper functions inside the Tests tab

Step 5: Send the request

Step 6: Observe the test results in the Postman Test Results tab

✅ Expected Result: The test results show that the status code is 200 and the response body contains a 'users' array

Automation Requirements - Postman Tests (JavaScript)

Assertions Needed:

Verify response status code is 200

Verify response body has a 'users' array

Best Practices:

Use reusable functions for common checks

Use pm.expect assertions for clear test results

Keep test code clean and readable

Automated Solution

Postman

function checkStatus200() {
    pm.test('Status code is 200', function () {
        pm.response.to.have.status(200);
    });
}

function checkUsersArray() {
    pm.test('Response has users array', function () {
        const jsonData = pm.response.json();
        pm.expect(jsonData).to.have.property('users').that.is.an('array');
    });
}

// Call utility functions
checkStatus200();
checkUsersArray();

The checkStatus200 function creates a test to verify the response status code is 200 using pm.response.to.have.status(200). This confirms the request succeeded.

The checkUsersArray function parses the JSON response and asserts that it has a property users which is an array. This checks the expected data structure.

Both functions are called in the Tests tab to keep the test code organized and reusable. Using pm.test and pm.expect provides clear pass/fail results in Postman.

Common Mistakes - 3 Pitfalls

Writing all assertions directly without reusable functions

Not parsing response JSON before accessing properties

Using incorrect assertion syntax like pm.response.status === 200

Bonus Challenge

Extend the test utilities to check that each user object in the 'users' array has 'id' and 'name' properties

Show Hint

Practice

1. What is the main purpose of using test utilities and helpers in Postman tests?

easy

A. To increase the number of test cases automatically

B. To make API requests faster

C. To simplify writing and maintaining tests by reusing code

D. To change the API endpoint dynamically

Solution

1. Step 1: Understand the role of helpers

   Helpers are small reusable functions that simplify test code and avoid repetition.

2. Step 2: Identify the main benefit

   They make tests easier to write and maintain by reusing common logic.

3. Final Answer:

   To simplify writing and maintaining tests by reusing code -> Option C

4. Quick Check:

   Helpers simplify tests = A [OK]

Hint: Helpers reduce repeated code in tests [OK]

Common Mistakes:

• Thinking helpers speed up API requests
• Believing helpers create more test cases automatically
• Confusing helpers with dynamic endpoint changes

2. Which of the following is the correct way to define a helper function in Postman test scripts?

easy

A. checkStatus(response) => response.status == 200

B. def checkStatus(response): return response.code == 200

C. var checkStatus = response => { response.code = 200 }

D. function checkStatus(response) { return response.code === 200; }

Solution

1. Step 1: Identify JavaScript syntax in Postman

   Postman test scripts use JavaScript, so function keyword is correct.

2. Step 2: Check function correctness

   function checkStatus(response) { return response.code === 200; } defines a function that returns true if response.code equals 200, which is valid.

3. Final Answer:

   function checkStatus(response) { return response.code === 200; } -> Option D

4. Quick Check:

   JavaScript function syntax = C [OK]

Hint: Use JavaScript function keyword for helpers [OK]

Common Mistakes:

• Using Python syntax in Postman scripts
• Using arrow function but with assignment errors
• Using single equals instead of triple equals

3. Given the helper function below, what will be the output of pm.test('Check status', () => { pm.expect(isSuccess({code: 200})).to.be.true; });?

function isSuccess(response) {
  return response.code === 200;
}

medium

A. Test passes because response code is 200

B. Test fails because response code is not 200

C. Syntax error in helper function

D. Runtime error due to undefined response

Solution

1. Step 1: Analyze helper function behavior

   The function returns true if response.code equals 200, which it does here.

2. Step 2: Evaluate test assertion

   The test expects isSuccess to be true, so the assertion passes.

3. Final Answer:

   Test passes because response code is 200 -> Option A

4. Quick Check:

   response.code === 200 -> true -> test passes [OK]

Hint: Check helper return value matches assertion [OK]

Common Mistakes:

• Assuming test fails without checking code value
• Confusing syntax error with correct JavaScript
• Thinking response is undefined when it is provided

4. You wrote this helper function in Postman tests but it throws an error:

function isValid(response) {
  return response.status = 200;
}

What is the error and how to fix it?

medium

A. Use '===' instead of '=' for comparison in return statement

B. Change function to arrow syntax

C. Remove the return keyword

D. Rename function to start with uppercase letter

Solution

1. Step 1: Identify assignment vs comparison

   The code uses '=' which assigns value instead of comparing.

2. Step 2: Correct the operator

   Replace '=' with '===' to compare response.status to 200.

3. Final Answer:

   Use '===' instead of '=' for comparison in return statement -> Option A

4. Quick Check:

   Comparison needs '===' not '=' [OK]

Hint: Use triple equals for comparisons in helpers [OK]

Common Mistakes:

• Confusing assignment '=' with comparison '==='
• Thinking arrow function fixes this error
• Removing return breaks function output

5. You want to create a helper that checks if a JSON response has a non-empty data array. Which helper function below correctly implements this check?

hard

A. function hasData(response) { return response.data == undefined; }

B. function hasData(response) { return Array.isArray(response.data) && response.data.length > 0; }

C. function hasData(response) { return response.data !== null; }

D. function hasData(response) { return response.data.length >= 0; }

Solution

1. Step 1: Check if response.data is an array

   Use Array.isArray to confirm data is an array.

2. Step 2: Verify array is not empty

   Check that length is greater than zero to ensure non-empty.

3. Final Answer:

   function hasData(response) { return Array.isArray(response.data) && response.data.length > 0; } -> Option B

4. Quick Check:

   Array check + length > 0 = D [OK]

Hint: Check array type and length > 0 for non-empty data [OK]

Common Mistakes:

• Only checking length without confirming array type
• Checking for null but ignoring empty arrays
• Using == undefined which is incorrect here