Top 15+ API and POSTMAN Interview Questions - Software Testing Study Materials

Here You will get API and POSTMAN Interview Questions and answers.

A well-liked API testing application called The Postman supports the development team in creating, sharing, and testing API documentation. In addition to a command-line utility for seasoned testers, the Postman tool offers a GUI interface for testing an API. You can construct the request with the aid of this API testing tool by following the API’s requirements. You can test the API from your browser by using the Chrome extension(Now no longer supported) that the Postman team has made available. No need to download the application from the official website.

What is API testing? Why is it important in the software development process?

API testing refers to the process of testing the functionality, reliability, performance, and security of application programming interfaces (APIs). APIs allow different software systems to communicate and interact with each other. API testing is important in the software development process because:

– It ensures that the API functions as intended and meets the expected requirements.

– It validates the behavior of the API by testing various input combinations and scenarios.

– It helps identify and fix issues related to functionality, performance, security, and integration.

– It promotes better communication and collaboration between different teams involved in software development.

– It enhances the overall quality and reliability of the software product.

What are the different types of API testing?

– Unit Testing: Testing individual components or units of code in isolation to ensure their correctness.

– Functional Testing: Testing the functional behavior of APIs by verifying if they produce the expected outputs for different inputs.

– Performance Testing: Testing the performance, scalability, and responsiveness of APIs under various load conditions.

– Security Testing: Testing the API for vulnerabilities, unauthorized access, data integrity, and encryption.

– Integration Testing: Testing the interaction between multiple APIs or the integration of APIs with other systems.

– Regression Testing: Testing the API after making changes to ensure that existing functionality has not been affected.

Explain the main differences between SOAP and RESTful APIs.

The main differences between SOAP and RESTful APIs are as follows:

SOAP (Simple Object Access Protocol) API:

– It is a protocol used for exchanging structured information over web services.

– SOAP APIs use XML (eXtensible Markup Language) for data formatting.

– SOAP APIs require a specific contract (WSDL) to define the operations and message formats.

– It supports more robust error handling, security, and reliable messaging.

– It is often used in enterprise environments and for complex integrations.

RESTful (Representational State Transfer) API:

– It is an architectural style for building web services.

– RESTful APIs use simple data formats such as JSON (JavaScript Object Notation) or XML.

– RESTful APIs are lightweight and use standard HTTP methods (GET, POST, PUT, DELETE) for communication.

– It follows the principles of statelessness, scalability, and caching.

– It is widely used in web and mobile applications due to its simplicity and ease of use.

What is Postman? How is it used in API testing?

Postman is a popular API development and testing tool that simplifies the process of testing APIs. It provides a user-friendly interface for sending HTTP requests, validating responses, and automating API testing. Postman offers features such as:

– Building and sending HTTP requests using various methods (GET, POST, PUT, PATCH, DELETE).

– Managing API endpoints and organizing them into collections for easier testing and collaboration.

– Handling request parameters, headers, authentication, and authorization mechanisms.

– Capturing and inspecting API responses, including headers, status codes, and response bodies.

– Writing and executing test scripts using JavaScript to validate API responses.

– Parameterizing requests and responses using variables for data-driven testing.

– Generating documentation for APIs to facilitate communication and usage.

– Integrating with CI/CD tools for continuous testing and automation.

Postman simplifies the testing process by providing a comprehensive and intuitive interface for API testing and development.

What are the common HTTP methods used in API testing?

Common HTTP methods used in API testing are:

– GET: Retrieves information from the server.

– POST: Sends data to the server to create a new resource.

– PUT: Updates an existing resource on the server.

– PATCH: Partially updates an existing resource on the server.

– DELETE: Deletes a resource from the server.

These HTTP methods provide the necessary functionality to perform CRUD (Create, Read, Update, Delete) operations on resources through API endpoints.

How do you define API endpoints in Postman?

API endpoints define the specific URL paths to access and interact with different resources or functionalities provided by an API. The structure of API endpoints plays a crucial role in ensuring the usability, scalability, and maintainability of the API. Here is a detailed explanation of API endpoint structure:

Base URL: The base URL is the root address that serves as the foundation for all API endpoints. It typically includes the protocol (HTTP or HTTPS) and the domain or IP address of the server hosting the API. For example, https://api.example.com.

Versioning (optional): To support backward compatibility and introduce changes without breaking existing integrations, APIs often include a version number in the URL. This helps differentiate between different versions of the API. For example, /v1 or /v2 can be appended to the base URL to denote different API versions.

Resource Path: The resource path represents the specific resource or functionality that the API endpoint exposes. It provides a hierarchical structure to organize and access different parts of the API. The resource path follows the base URL and versioning (if applicable) and may include multiple segments separated by forward slashes (“/”).

Path Parameters:

Path parameters are dynamic placeholders within the resource path that are replaced with actual values when making an API request. They provide a way to identify and retrieve specific instances of a resource. Path parameters are usually denoted with curly braces ({}) and contain a parameter name. For example, /users/{userId} allows accessing a specific user by replacing {userId} with the actual user ID.

Query Parameters: Query parameters are used to pass additional information to the API endpoint as key-value pairs. They follow the resource path and are separate from it by a question mark (?). Multiple query parameters can be added, separate by ampersands (&). Query parameters are optional and allow filtering, sorting, pagination, or specifying other preferences for the API response. For example, /products?category=electronics&sort=price.

HTTP Methods: HTTP methods or verbs indicate the type of action performed on the resource defined by the API endpoint. The commonly used HTTP methods in API testing are GET, POST, PUT, PATCH, and DELETE. The choice of HTTP method depends on the intended action, such as retrieving data (GET), creating a new resource (POST), updating an existing resource (PUT, PATCH), or deleting a resource (DELETE).

Headers: Headers provide additional information about the API request or response. They include metadata, authentication tokens, content type, caching instructions, or custom data. Common headers include Content-Type, Authorization, and Accept. Headers can be specifie in API requests to communicate specific requirements or expectations.

Request Body (optional): For certain HTTP methods like POST or PUT, the API endpoint may accept a request body containing additional data. The request body can be in various formats, such as JSON, XML, or form-urlencoded. It allows sending complex data structures or payload to the API server.

How do you handle authentication and authorization in API testing using Postman?

Postman provides various options for handling authentication and authorization in API testing. Some common methods include:

– Basic Authentication: Providing username and password in the request headers.

– Bearer Token Authentication: Sending a token in the request headers (commonly used for OAuth).

– API Key Authentication: Including an API key in the request headers or as a query parameter.

– Digest Authentication: Authenticating using a username, password, and nonce value.

– OAuth Authentication: Configuring OAuth 1.0 or OAuth 2.0 flows within Postman.

You can configure authentication methods for individual requests or set up authentication at the collection or environment level to apply it to multiple requests. Postman provides a user-friendly interface to configure authentication parameters and store sensitive data securely.

What is the purpose of status codes in API responses? Give examples of commonly used status codes.

Status codes in API responses indicate the outcome or status of a request. Some commonly used status codes include:

Certainly! Here are a few more commonly used status codes from the 2xx, 3xx, 4xx, and 5xx series:

2xx Success:

– 200 OK: The request was successful, and the server returned the requested data.

– 201 Created: The request was successful, and a new resource was create.

– 204 No Content: The request was successful, but there is no data to return in the response body.

3xx Redirection:

– 301 Moved Permanently: The requested resource has been permanently moved to a different location.

– 302 Found: The requested resource has been temporarily moved to a different location.

– 304 Not Modified: The client’s cached version of the requested resource is still valid.

4xx Client Errors:

– 400 Bad Request: The server could not process the request due to client error or invalid input.

– 401 Unauthorized: The request requires authentication, and the provided credentials are missing or invalid.

– 403 Forbidden: The server understood the request, but the client does not have permission to access the resource.

– 404 Not Found: The request resource could not be found on the server.

5xx Server Errors:

– 500 Internal Server Error: The server encounters an unexpected error while processing the request.

– 502 Bad Gateway: The server acting as a gateway or proxy receives an invalid response from an upstream server.

– 503 Service Unavailable: The server is temporarily unavailable, often due to maintenance or high load.

– 504 Gateway Timeout: The server acting as a gateway or proxy did not receive a timely response from an upstream server.

These status codes provide additional information about the outcome of API requests, including success, redirection, client errors, and server errors.

Status codes provide information about the success, failure, or specific conditions of the API request, aiding in error handling, debugging, and understanding the API’s behavior.

How do you handle errors and exceptions in API testing?

When handling errors and exceptions in API testing, it is essential to consider:

– Proper error messaging: Ensure that error responses include informative and clear error messages that help identify the issue.

– Error status codes: Validate that the API returns the appropriate HTTP status codes for different error scenarios (e.g., 400 for validation errors, 404 for not found).

– Exception handling: Test how the API handles exceptional cases such as timeouts, connection failures, or invalid requests.

– Error response formats: Verify that error responses follow a consistent format (e.g., JSON) and provide relevant information like error codes and descriptions.

What do you test in API testing which parameters do you check while hitting endpoints in Postman?

In API testing, you test various aspects while hitting endpoints in Postman, including:

– Request parameters: Check if the API correctly handles different combinations of query parameters, path parameters, and headers.

– Request payload: Test the handling of different types of request payloads (e.g., JSON, XML) and ensure proper validation and processing.

– Authentication and authorization: Verify that the

API correctly authenticates and authorizes requests based on the provided credentials or tokens.

– Response validation: Validate the structure, format, and data of the API responses to ensure they match the expected results.

– Status codes: Verify that the API returns the appropriate status codes for different scenarios, such as success, failure, or invalid requests.

– Error handling: Test how the API handles and returns errors, including error messages, status codes, and error response formats.

– Performance and scalability: Evaluate the API’s performance under various load conditions to ensure it can handle a significant number of requests.

These parameters cover various aspects of API testing and help ensure the API functions correctly, performs well and provides a satisfactory user experience.

What are the main challenges you may face when testing APIs

When testing APIs, some of the main challenges you may face include:

– API versioning: Managing different versions of the API and ensuring backward compatibility.

– Complex data structures: Testing APIs that handle complex data structures or nested JSON/XML payloads.

– Integration with external systems: Testing APIs that integrate with third-party services or external databases.

– Authentication and authorization: Ensuring proper authentication and authorization mechanisms are in place and working correctly.

– Error handling and exceptions: Testing how the API handles and reports errors or exceptions in different scenarios.

– Performance and scalability: Evaluating the performance and scalability of the API under varying load conditions.

– Security vulnerabilities: Identifying and addressing potential security vulnerabilities, such as injections or unauthorize access.

– API documentation: Ensuring the API documentation accurately reflects the API’s behavior and functionality.

Overcoming these challenges requires thorough testing strategies, clear communication, collaboration, and staying update with the latest testing techniques and tools.

Explain the process of parameterization(Path parameters and query parameters) in API testing using Postman.

Parameterization in API testing involves substituting dynamic values for certain parameters to test different scenarios. In Postman, parameterization can be achieve using path parameters and query parameters. Here’s an explanation of the process:

– Path parameters: Path parameters are placeholders in the API URL that are replace with actual values during the request. To parameterize path parameters in Postman:

– Define a variable within Postman, such as {{userId}}, to represent the dynamic value.

– Modify the API URL to include the variable as part of the path, for example, `/users/{{userId}}`.

– During the request execution, replace the variable with the desired value in the Postman request or use scripting to assign the value dynamically.

– Query parameters: Query parameters are used to send additional information with the API request. To parameterize query parameters in Postman:

– Define a variable within Postman, such as {{searchTerm}}, to represent the dynamic value.

– Include the variable in the query parameter section of the request URL, for example, `?q={{searchTerm}}`.

– Set the value of the variable before executing the request, either manually or through scripting.

By parameterizing path and query parameters, you can test different variations of API requests without modifying the request URL each time, improving testing efficiency and coverage.

What is a collection in Postman, and how is it useful in API testing?

In Postman, a collection is a container that holds a group of related API requests. It provides a structured way to organize and manage your API tests. Collections are useful in API testing for the following reasons:

– Organization: Collections allow you to group related API requests together, making it easier to navigate and manage your tests.

– Reusability: You can reuse collections across different projects or share them with team members, promoting collaboration and efficiency.

– Test execution: Collections enable you to execute multiple API requests in a sequence, simulating a series of steps or test scenarios.

– Test automation: You can automate the execution of collections using Postman’s collection runner or integrate them into continuous integration and delivery (CI/CD) pipelines.

– Test reporting: Collections provide consolidated test reports, allowing you to analyze the results of multiple API tests together. – Documentation: Collections can be used to generate API documentation, providing a clear overview of the available endpoints and their usage.

What are the benefits of using environment variables in API testing with Postman?

Environment variables in Postman are placeholders that hold values specific to a particular environment. Using environment variables in API testing with Postman provides several benefits:

– Reusability: Environment variables allow you to define values once and reuse them across multiple requests or collections.

– Flexibility: You can easily switch between different environments (e.g., development, staging, production) by changing the values of the environment variables.

– Security: Environment variables provide a secure way to store sensitive data such as API keys, tokens, or passwords, as they can be encrypted or hidden.

– Scalability: As your testing environment grows, managing and updating values across multiple requests becomes more manageable with environment variables.

– Collaboration: Environment variables can be shared with team members, ensuring consistency and reducing the need to manually update values in multiple places.

By utilizing environment variables, you can streamline your testing efforts, improve maintainability, and enhance collaboration among team members.

How do you define and use environment variables in Postman?

To define and use environment variables in Postman:

– Create an environment: In Postman, create a new environment or select an existing one that corresponds to your test environment (e.g., development, staging, production).

– Define variables: Within the environment, define variables by providing a key-value pair. For example, key: `baseURL`, value: `https://api.example.com`.

– Use variables in requests: In your API requests, use the defined variables by enclosing the variable name within double curly braces (`{{}}`). For example, `{{baseURL}}/users`.

– Switch environments: To switch between different environments, select the desired environment from the environment dropdown menu.

Update variable values: If you need to update the value of an environment variable, you can do so within the environment settings. The updated value will automatically propagate to all requests that use that variable.

– Global and local variables: Postman allows you to define variables at both the global and local levels. Global variables are accessible across all environments, while local variables are specific to a particular environment.

– Pre-request scripts and tests: You can use pre-request scripts and tests to dynamically set or modify the values of environment variables based on certain conditions or calculations.

By leveraging environment variables, you can easily switch between different environments, maintain consistency in your tests, and keep sensitive information secure.

What is JSON, and why is it commonly used in API testing?

JSON (JavaScript Object Notation) is a lightweight data interchange format commonly used in API testing. It is easy to read and write for humans and easy to parse and generate for machines. JSON is widely used in API testing due to the following reasons:

– Simplicity: JSON uses a straightforward syntax consisting of key-value pairs, arrays, and nested objects, making it easy to understand and work with.

– Compatibility: JSON is supported by most programming languages, making it a suitable choice for data exchange between different systems.

– Lightweight: JSON has a compact format, resulting in smaller payload sizes compared to other formats like XML, which improves network efficiency.

– Readability: JSON is human-readable, which simplifies debugging and troubleshooting during API testing.

– Language independence: JSON is language-independent, meaning it can be used across various programming languages and platforms.

– Data structure representation: JSON’s structure closely resembles that of many programming languages, making it intuitive to map JSON data to objects or data structures.

Due to its simplicity, compatibility, and readability, JSON has become the preferred choice for representing data in API requests and responses.

How do you handle JSON payloads in API requests and responses using Postman?

Postman provides features to handle JSON payloads in API requests and responses efficiently. Here’s how you can work with JSON in Postman:

– Sending JSON requests: In Postman, you can include JSON data in the request body by selecting the appropriate content type (e.g., application/json) and providing the JSON payload as a string or object.

– Dynamic values: Postman allows you to use environment variables or define variables within Postman itself to substitute dynamic values in JSON payloads. This enables parameterization and data-driven testing.

– JSON validation: Postman allows you to validate the structure and schema of JSON responses using assertions. You can verify specific properties, values, or nested structures within the JSON response.

– JSON manipulation: Postman provides scripting capabilities using JavaScript, allowing you to extract specific data from JSON responses and use them in subsequent requests.

– Pretty-printing: Postman automatically formats JSON responses to make them more readable. You can also use external tools or Postman’s built-in prettify option to format JSON payloads for better readability.

By leveraging these features, you can easily work with JSON payloads, validate responses, extract data, and ensure the correctness of your API tests.

Roles and responsibilities of API tester

The roles and responsibilities of an API tester may vary depending on the organization and project. However, some common roles and responsibilities of an API tester include:

– Understanding API requirements: Collaborating with stakeholders to understand the functional and non-functional requirements of the API.

– Test planning and design: Creating a comprehensive test strategy, test plan, and test cases based on the API requirements.

– Test execution: Executing API tests using testing tools like Postman, validating request and response behavior, and capturing test results.

– Test automation: Developing and maintaining automated test scripts using tools like Postman, Newman, or scripting languages to perform regression testing and continuous integration.

– API documentation: Ensuring that API documentation accurately reflects the behavior and usage of the API, including request/response examples and guidelines for other developers.

– Performance testing: Conducting performance testing to measure the API’s response time, throughput, and scalability under different load conditions.

– Security testing: Identifying and testing potential security vulnerabilities, such as injections, authentication flaws, or data exposure, and collaborating with security teams to address them.

– Defect management: Identifying, documenting, and tracking defects found during testing, and working closely with developers to resolve them.

– Collaboration and communication: Collaborating with developers, business analysts, and other stakeholders to clarify requirements, report issues, and ensure smooth communication throughout the testing process.

– Continuous improvement: Staying updated with industry trends, best practices, and new tools and techniques for API testing, and continuously improving testing processes and methodologies.

These responsibilities highlight the important role an API tester plays in ensuring the quality, reliability, and security of the API being tested.