Variable syntax ({{variable}}) in Postman - Build an Automation Script

Verify usage of variable syntax {{variable}} in Postman request

Preconditions (2)

Step 1: Open the Postman collection

Step 2: Select the request that uses the URL with {{userId}} variable, e.g., https://api.example.com/users/{{userId}}

Step 3: Send the request

Step 4: Observe the request URL in the Postman console or request details

✅ Expected Result: The request URL should replace {{userId}} with the value '12345' from the environment variable, resulting in https://api.example.com/users/12345

Automation Requirements - Postman test scripts (JavaScript)

Assertions Needed:

Verify that the request URL contains the variable value '12345' instead of the literal '{{userId}}'

Verify the response status code is 200

Best Practices:

Use pm.environment.get('userId') to access variable values

Use pm.test() blocks for assertions

Avoid hardcoding variable values in tests; use environment variables

Log useful information with console.log for debugging

Automated Solution

Postman

pm.test('Request URL uses variable value', function () {
    const requestUrl = pm.request.url.toString();
    const userId = pm.environment.get('userId');
    pm.expect(requestUrl).to.include(userId);
    pm.expect(requestUrl).to.not.include('{{userId}}');
});

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

The first test checks that the request URL contains the actual value of the environment variable 'userId' instead of the literal string '{{userId}}'. This confirms that Postman correctly replaced the variable syntax before sending the request.

The second test verifies that the response status code is 200, indicating the request was successful.

Using pm.environment.get('userId') ensures the test dynamically uses the variable value from the environment, making the test flexible and maintainable.

Assertions are wrapped in pm.test() blocks for clear reporting in Postman test results.

Common Mistakes - 3 Pitfalls

{'mistake': "Checking for the literal string '{{userId}}' in the request URL instead of the replaced value", 'why_bad': 'This does not verify that the variable was replaced; it only checks the raw template string.', 'correct_approach': "Check that the request URL contains the actual variable value from the environment and does not contain the literal '{{userId}}'."}

{'mistake': 'Hardcoding the variable value in the test instead of retrieving it from the environment', 'why_bad': 'Makes tests brittle and not reusable if the variable value changes.', 'correct_approach': "Use pm.environment.get('userId') to get the current value dynamically."}

Not verifying the response status code

Bonus Challenge

Now add data-driven testing with 3 different userId values to verify variable replacement and response success for each.

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