10 API Testing with Postman Interview Questions and Answers

API testing is a critical aspect of modern software development, ensuring that applications communicate effectively and reliably. Postman has emerged as a popular tool for API testing due to its user-friendly interface, extensive feature set, and robust support for automated testing. It allows developers and testers to create, share, and manage API requests and responses with ease, making it an essential tool in the software development lifecycle.

This article provides a curated selection of interview questions and answers focused on API testing with Postman. By familiarizing yourself with these questions, you will gain a deeper understanding of key concepts and best practices, enhancing your ability to demonstrate proficiency in API testing during your interviews.

API Testing with Postman Interview Questions and Answers

1. What is Postman and how does it facilitate API testing?

Postman is an API development environment that simplifies testing and interacting with APIs. It allows users to create and send HTTP requests and view responses. Supporting various HTTP methods like GET, POST, PUT, and DELETE, Postman is versatile for different API interactions. Users can organize requests into collections, which can be saved for reuse. Environment variables enable easy switching between different settings, such as development and production, without manually changing request parameters. Postman’s built-in testing capabilities allow users to write JavaScript scripts to validate API responses, checking for status codes, response times, and specific data in the response body.

2. How do you use environment variables in Postman?

Environment variables in Postman store data that can change based on different environments, such as API endpoints or authentication tokens. This allows users to switch between environments without altering requests. To use them, create an environment, add key-value pairs, and reference these variables in requests using double curly braces, e.g., {{base_url}}. Before sending a request, select the appropriate environment.

Example:

– Create an environment named “Development” with a variable base_url set to https://dev.api.example.com.
– Use {{base_url}}/endpoint as the URL in your request.
– Select the “Development” environment and send the request.

{
  "method": "GET",
  "url": "{{base_url}}/users",
  "headers": {
    "Authorization": "Bearer {{auth_token}}"
  }
}

3. Write a basic test script in Postman using JavaScript.

In Postman, you can write test scripts using JavaScript to validate API behavior. Here is a basic example that checks if the response status code is 200 and if the response time is within acceptable limits.

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

pm.test("Response time is less than 200ms", function () {
    pm.expect(pm.response.responseTime).to.be.below(200);
});

4. Write a script to check if an API response contains a specific JSON key-value pair.

To check if an API response contains a specific JSON key-value pair, use the pm object in Postman’s JavaScript environment. Here’s a script that checks for a specific key-value pair:

// Example: Check if the response contains the key-value pair "status": "success"
pm.test("Response contains status: success", function () {
    var jsonData = pm.response.json();
    pm.expect(jsonData.status).to.eql("success");
});

In this script:
– pm.response.json() parses the response body as JSON.
– pm.test defines a test case.
– pm.expect asserts that the value of the status key is “success”.

5. Explain how to use Postman’s pre-request scripts.

Pre-request scripts in Postman run JavaScript code before a request is sent. They can set up environment variables, generate tokens, or modify request parameters dynamically.

Example:

// Generate a random number and set it as an environment variable
const randomNumber = Math.floor(Math.random() * 1000);
pm.environment.set("randomNumber", randomNumber);

// Set the current timestamp as an environment variable
const timestamp = new Date().toISOString();
pm.environment.set("timestamp", timestamp);

// Example of generating an authentication token
const username = pm.environment.get("username");
const password = pm.environment.get("password");
const authToken = btoa(`${username}:${password}`);
pm.environment.set("authToken", authToken);

6. Write a script to validate the status code and response time of an API request.

To validate the status code and response time of an API request in Postman, use the following script in the “Tests” tab:

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

pm.test("Response time is less than 200ms", function () {
    pm.expect(pm.response.responseTime).to.be.below(200);
});

The first test checks if the status code is 200, indicating a successful request. The second test ensures the response time is under 200 milliseconds.

7. How do you integrate Postman with CI/CD pipelines?

Integrating Postman with CI/CD pipelines involves using Newman, Postman’s command-line tool, to run collections as part of the automated build and deployment process. This ensures API tests are executed automatically, providing immediate feedback on API health.

Steps to integrate Postman with a CI/CD pipeline:

– Export your Postman collection and environment.
– Install Newman.
– Configure your CI/CD pipeline to use Newman to run the exported collection.

Example in a Jenkins pipeline:

pipeline {
    agent any

    stages {
        stage('Test') {
            steps {
                script {
                    sh 'newman run your_postman_collection.json -e your_postman_environment.json'
                }
            }
        }
    }
}

8. Write a script to chain multiple requests together and pass data between them.

In Postman, chaining multiple requests and passing data between them can be achieved using pre-request and test scripts. This allows you to extract data from one request’s response and use it in subsequent requests.

Example:

– First Request: Get a token
– Second Request: Use the token to access a protected resource

// First Request: Get a token
pm.test("Extract token", function () {
    var jsonData = pm.response.json();
    pm.environment.set("authToken", jsonData.token);
});

// Second Request: Use the token
pm.request.headers.add({
    key: "Authorization",
    value: "Bearer " + pm.environment.get("authToken")
});

In the first request, extract the token from the response and store it in an environment variable. In the second request, use this token by adding it to the request headers.

9. What are mock servers in Postman and how are they used?

Mock servers in Postman simulate an API, useful for testing and development when the actual API is unavailable. They allow you to define expected API behavior, including endpoints, request parameters, and responses.

To create a mock server in Postman:

1. Create or use an existing collection.
2. Add requests to the collection to mock.
3. Define expected responses for these requests.
4. Use the Mock Server option to generate a mock server URL.
5. Use this URL in your application or tests to simulate API behavior.

Mock servers are useful for frontend developers working on the UI without the backend, testing different scenarios, and isolating issues by simulating specific API behaviors.

10. How do you test SOAP APIs using Postman?

To test SOAP APIs using Postman, configure your requests properly. SOAP (Simple Object Access Protocol) is a protocol for exchanging structured information in web services. Postman can test SOAP APIs with some configuration.

– Set the Request Type to POST: SOAP APIs typically use POST requests.
– Set the Request URL: Enter the endpoint URL of the SOAP API.
– Set the Headers: Set the Content-Type header to text/xml or application/soap+xml.
– Add the SOAP Envelope: Include the SOAP envelope in the request body. Select “raw” and set the format to “XML” in Postman.
– Send the Request and Validate the Response: Postman will display the response in XML format, and you can use its features to validate the response data.

Example SOAP Envelope:

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:web="http://www.example.com/webservice">
   <soapenv:Header/>
   <soapenv:Body>
      <web:GetExample>
         <web:Parameter>Value</web:Parameter>
      </web:GetExample>
   </soapenv:Body>
</soapenv:Envelope>