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Table of contents
1.
Introduction
2.
Commonly Asked API Testing Interview Questions
2.1.
1. What exactly is API?
2.2.
2. What is API testing, and why is it important?
2.3.
3. How do APIs function?
2.4.
4. How does API testing work?
2.5.
5. What protocols can API Testing be used to test?
2.6.
6. What architectural styles are available for creating a Web API?
2.7.
7. What are the various API testing types?
2.8.
8. What is the distinction between APIs and Web services?
2.9.
9. What are the design principles for an API test?
2.10.
10. Which API testing tools are most commonly used?
2.11.
11. What are the limitations of using APIs?
2.12.
12. What exactly is soap?
2.13.
13. When performing API testing, what should be checked?
2.14.
14. What are the distinctions between API and Unit Testing?
2.15.
15. What are some of the benefits of API testing?
2.16.
16. What role does the caching mechanism play?
2.17.
17. What is the benefit of automated API testing?
2.18.
18. What are the distinctions between API and UI testing?
2.19.
19. What exactly do you mean when you say "black box testing"?
2.20.
20. What is an API framework, and how does it work?
2.21.
21. What types of API tests are commonly performed?
2.22.
22. What are the most challenging aspects of API testing?
2.23.
23. What does API documentation entail?
2.24.
24. What makes API testing the best option for automation testing?
2.25.
25. What are the most commonly found API errors?
2.26.
26. How frequently are APIs updated, and, more importantly, deprecated?
2.27.
27. In performance testing, what exactly do you mean by throughput?
2.28.
28. What exactly is Rest API?
2.29.
29. What's the distinction between SOAP and RESTful?
2.30.
30. What components make up an HTTP request?
2.31.
31. What is the HTTP protocol that REST supports?
2.32.
32. For RESTful Web services, what is the function of the OPTIONS method?
2.33.
33. What is the definition of URI? What is the purpose and format of REST-based web services?
2.34.
34. How do the PUT and POST methods differ?
2.35.
35. How should the API security be tested?
2.36.
36. How do you go about doing API load testing?
2.37.
37. Explain OAuth 2.0 Authentication
2.38.
38. Explain how to handle security testing for an API that requires authentication and authorization.
2.39.
39. What are the challenges of testing microservices-based APIs, and how can you overcome them?
2.40.
40. What factors need to be taken into account while load testing a RESTful API?
3.
Frequently Asked Questions
3.1.
How do you explain API testing in an interview? 
3.2.
What are basic interview questions API testing? 
3.3.
What are the 3 types of testing in API? 
3.4.
What are the 4 method API testing?
3.5.
What are the 4 methods of API testing?
3.6.
What are the 5 HTTP methods?
4.
Conclusion
Last Updated: May 21, 2024
Easy

Top 40 API Testing Interview Questions and Answers (2024)

Author Palak Mishra
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Speaker
Ashwin Goyal
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18 Jun, 2024 @ 01:30 PM

Introduction

APIs (Application Programming Interfaces) play a crucial role in modern software development, facilitating seamless communication and integration between different software systems. As API usage continues to rise, so does the demand for proficient API testers who can ensure the reliability, functionality, and security of these interfaces.

api testing interview questions

API testing is a type of software testing that directly tests application programming interfaces (APIs) and integrates them to see if they meet functionality, reliability, performance, and security requirements. Because APIs lack a graphical user interface, testing is done at the message layer, where application logic can be validated quickly and effectively.

Let's get started with API Testing Interview Questions!

Commonly Asked API Testing Interview Questions

1. What exactly is API?

Ans: API (Application Programming Interface) facilitates data exchange and communication between two software systems. APIs serve as a connection point between two applications, allowing them to communicate. A programming interface (API) is a set of functions that another program can call.

The API takes a request from the source, sends it to the database, retrieves the data, and returns a response to the source. The API takes the user's requests and responds without revealing the internal details. API provides abstraction.

Example: a. Log-in Using XYZ  b. Weather Snippets  c. Make a PayPal payment  d. Bots on Twitter  e. travel booking

2. What is API testing, and why is it important?

Ans: API testing is software integration testing that focuses on application programming interfaces (APIs). It is concerned with determining whether the APIs developed are reliable, functional, secure, and perform as expected in terms of the business logic covered by the applications.

3. How do APIs function?

Ans: The general API workflow is that it receives a request, processes it (which may include data validation, database interaction, and data processing), and then sends the result back to the source. Because APIs are not exposed to the outside world, they provide an abstraction for internal business logic.

4. How does API testing work?

Ans: Setting up an API's test environment is a difficult task, so you should be prepared with an answer if your API testing interview is approaching. API's test environment is reasonably comprehensive, requiring database and server configuration based on software requirements. This test form does not have any GUI (Graphical User Interface).

API is checked for proper operation after the installation process is completed. Different parameters are set up in the API called from the original environment to study the test results throughout the process.

5. What protocols can API Testing be used to test?

Ans: Some of the most popular API testing protocols are as follows:

  • HTTP.
  • JSON-RPC.
  • REST.
  • SOAP.
  • JMS.
  • UDDI.
  • XML-RPC.

6. What architectural styles are available for creating a Web API?

Ans: The following are some architectural styles for developing web APIs.

  • The address for the services is a simple URI.
  • Communication without boundaries
  • Client-server communication using HTTP
  • Formatting language: XML/JSON

7. What are the various API testing types?

Ans: API testing can be divided into several categories:

  • Functional Testing
  • Unit Testing
  • Load Testing
  • Testing for security
  • User Interface Testing
  • Testing for interoperability and WS compliance
  • Testing for Penetration (Pen Test)
  • Testing for Fuzz

8. What is the distinction between APIs and Web services?

Ans:

Web-based services:

  • 1. Web services are all APIs.
  • 2. All web services must be accessible via the internet (HTTP)
  • 3. There are only three ways to use a Web service: Communication protocols include SOAP, REST, and XML-RPC.
  • 4. A Web service requires a network to function.
     

APIs:

  • 1. Web services are not all APIs.
  • 2. Not all APIs must be accessible through the internet (i.e., HTTP)
  • 3. APIs communicate in various ways, including DLL files in C/C++, Jar files/ RMI in Java, and Linux kernel API interrupts.
  • 4. APIs work without the use of a network.

9. What are the design principles for an API test?

Ans: The five most important API test design principles are as follows:

  • Setup: Create objects, start services, initialize data
  • Execution: Steps to use the API or run the scenario, including logging
  • Verification: Oracles will assess the execution's outcome.
  • Reporting: successful, unsuccessful, or blocked
  • Cleaning: Pre-test state

10. Which API testing tools are most commonly used?

Ans: PostMan is the most widely used tool available. This tool assists in developing manual and automated test cases for properly testing APIs. Other tools include JMeter, Parasoft SOAtest, SoapUI, Apigee, API Fortress, JUnit, etc.

11. What are the limitations of using APIs?

Ans: The provider of many APIs has imposed a limit. As a result, try to estimate our usage and see how it will affect the overall cost of the service.

12. What exactly is soap?

Ans: The acronym SOAP refers to the Simple Object Access Protocol. It is a messaging protocol based on XML. It facilitates the exchange of data between computers.

13. When performing API testing, what should be checked?

Ans: A request is made to the API with the known data during the API testing process. You can then examine the validation response in this manner. 

Consider the following when testing an API:

  • Data consistency
  • Validating a schema
  • HTTP status codes are a set of characters that describe how the server is
  • Order, completeness, and data type
  • Checks for authorization
  • Response timeouts are implemented.
  • If the API returns an error code, as well as
  • Performance and security testing are non-functional tests.

14. What are the distinctions between API and Unit Testing?

Ans:  API Testing

  • The Quality Analysts are in charge of this testing.
  • This falls under the heading of black-box testing.
  • API testing considers all system functionality because external developers will use the API.
  • The testers do not have access to the internal source code during this testing, and it is solely focused on the API's functionality.
     

UNIT Testing

  • The developers working on the corresponding modules are in charge of this testing.
  • This is a type of white box testing.
  • This testing verifies whether the unit of code works as expected or not in isolation, as the name implies.
  • Developers who work on unit test cases have access to the source code because they must ensure that the modules they develop pass before they are delivered.

15. What are some of the benefits of API testing?

Ans: API testing has the following benefits:

  • API testing allows you to access the application without using the user interface. Before the GUI tests, the application's core functionality will be tested. This will aid in the detection of minor issues that may become more serious during GUI testing.
     
  • API testing takes significantly less time than GUI testing. API testing, in particular, requires less code and thus provides better and faster test coverage than GUI test automation. This will lower the testing project's cost.
     
  • API testing data is exchanged using XML or JSON, regardless of the language. These transfer modes are completely language agnostic, allowing users to use any coding language when using the automation test service for their project.
     
  • API tests are easily integrated with GUI tests, making them helpful in performing functional GUI tests after GUI tests. Simple integration would allow for creating new user accounts within the application before the GUI was launched.

16. What role does the caching mechanism play?

Ans: The practice of temporarily storing data in order to retrieve it for subsequent requests is known as caching. This improves system performance by retrieving data from the cached copy rather than hitting the database and retrieving the original data.

17. What is the benefit of automated API testing?

Ans: Automated testing is beneficial in the long run because it helps to maximize application test coverage in a shorter amount of time, allowing large test sets to be tested quickly and easily. It allows for parallel processing and helps to reduce human error in testing. It reduces the time required to test applications, lowering the overall cost.

18. What are the distinctions between API and UI testing?

Ans: APIs allow two software systems to communicate with each other. An API-implemented software system contains functions or subroutines that another software system can execute.

On the other hand, UI (User Interface) testing refers to graphical interface testing, such as how users interact with applications and application elements such as fonts, images, and layouts. The look and feel of an application is the focus of UI testing.

19. What exactly do you mean when you say "black box testing"?

Ans: Black Box Testing is a type of software testing in which the testers assess the software's functionality without knowing the internal source code. 

Unit, integration, system, and acceptance testing can all benefit from this philosophy.

black box testing

20. What is an API framework, and how does it work?

Ans: A framework, also known as a software framework, is an application development platform. A software developer can build applications for a specific forum using an API framework as a foundation.

A framework, for example, can contain predefined classes and functions for processing input, managing hardware devices, and interacting with system software.

An Application Programming Interface (API) is similar to a framework, but a framework includes API. The framework provides the foundation for programming, while the API gives users access to the framework's elements. Code libraries, compilers, and other software development programs are part of the framework.

API framework is defined by a configuration file containing a list of all APIs that must be activated for a program to run.

21. What types of API tests are commonly performed?

Ans: We run the following API tests on a regular basis.

  • Check to see if the return value matches the input condition. The API responses should be checked against the request.
  • Check if the system authenticates the result when the API updates any data structure.
  • Check to see if the API causes other events or requests another API.
  • Test the API's behavior when there is no return value.

22. What are the most challenging aspects of API testing?

Ans: If you can overcome the challenges of API testing, you can be confident in your API testing interview. They are:

  • Parameter Selection
  • Parameter Combination
  • Call sequencing
  • Validation and verification of the output
  • Another significant difficulty is providing input values without a GUI.

23. What does API documentation entail?

Ans: Any foundation must have adequate documentation. API documentation is a handy reference for getting into a library or working with a program.

When we use such documents, they must have a proper plan, content source, layout, and information related to each function, among other things.

Doxygen and JavaDoc are examples of documentation tools. 

Here are the documented functions that revolve around parameters like:

  • Description of the function:
  • Error message type and syntax
  • For each parameter, syntax, elements, and sequence are required.
  • Functioning links

24. What makes API testing the best option for automation testing?

Ans: API testing is now considered more appropriate than GUI testing because:

  • It thoroughly verifies the system's functional paths.
  • The interface is the most stable.
  • It's easier to keep up with and gives immediate feedback.

25. What are the most commonly found API errors?

Ans: The interviewer will ask about API errors in a Web API testing interview to determine your knowledge and experience. 

The following are the most common:

  • Errors due to a missing module
  • Inconsistencies in documentation
  • Validation errors with parameters
  • And some standard error expectations, such as the occurrence of errors if the result is not as predicted, and the same warnings are specified in the form of a message. Within a single module, there could be one or more warnings.

26. How frequently are APIs updated, and, more importantly, deprecated?

Ans: APIs, exceptionally modern RESTful APIs, are a wonderful invention that can significantly simplify and accelerate integration efforts, increasing the likelihood that you will benefit from them. However, APIs can and do change for various reasons, sometimes abruptly, so REST APIs are no different in this regard from traditional integration methods. Your procedure will be interrupted if an API call becomes obsolete and disappears, so it's crucial to know how frequently the APIs you use change or are deprecated.

27. In performance testing, what exactly do you mean by throughput?

Ans: The number of transactions per second that an application can handle when many users interact is referred to as throughput (load). Before going live in production, the API must ensure that the required throughput is met. Load testing of the APIs can help us figure this out. We can do this by identifying multiple transactions with varying priorities and determining how many requests are completed within the SLAs (Service Level Agreements) that we have defined.

28. What exactly is Rest API?

Ans: Representational State Transfer is the acronym for Representational State Transfer. It's a collection of functions that aid developers in making requests and receiving responses. The REST API uses the HTTP protocol for interaction.

Read more about: SAP FICO Interview Questions

29. What's the distinction between SOAP and RESTful?

Ans: SOAP (Simple Object Access Protocol) :

  • SOAP is a protocol for exchanging XML documents between two computers.
  • Only the XML format is supported by SOAP.
  • Caching is not supported by SOAP.
  • SOAP is more time-consuming than REST.
  • SOAP is similar to a custom desktop application linked to the server.
  • SOAP uses HTTP, but it encapsulates the message.
     

RESTful:

  • REST is a network-based software architecture service architecture and design.
  • REST accepts a variety of data formats.
  • Caching is supported by REST.
  • REST is more efficient than SOAP.
  • The REST client is similar to a browser in that it uses standard methods. It must be able to accommodate an application.
  • HTTP headers are used by REST to store metadata.

30. What components make up an HTTP request?

Ans: There are five parts to an HTTP request. These are they:

  • GET, PUT, POST, and DELETE are examples of HTTP methods.
  • The URI (Uniform Resource Identifier) is the identifier for the server's resource.
  • Indicate the HTTP version, for example, HTTP V1.1.
  • Request Header: The HTTP request message's metadata is carried in the Request Header. A client's type, supported formats, message body format, cache setting, and so on are all examples of metadata.
  • The resource body indicates the message content or representation of the resource.

31. What is the HTTP protocol that REST supports?

Ans:

  • GET: This method is used to request data from a given resource.
    It is possible to cache and bookmark GET requests. It is saved in the browser history and is limited in length. GET requests should not be used when dealing with sensitive data.
     
  • POST: It is a method of sending data to a server to create r update resources.
    POST requests are never cached or saved in the browser.
     
  • PUT: It replaces the target resource's current representation with the request payload.
     
  • DELETE: This command deletes the specified resource.
     
  • OPTIONS: This word describes the target resources' communication options.
     
  • HEAD: It requests the same response as GET requests, but without the response body.

32. For RESTful Web services, what is the function of the OPTIONS method?

Ans: The choices method in RESTful Web services is used to get details about the communication choices accessible for a specific resource. Without actively acting on the resource, it enables a client to learn about the HTTP methods, headers, and other capabilities that are supported by a resource. This can be useful for learning how to use a certain resource and comprehending its functionalities.

33. What is the definition of URI? What is the purpose and format of REST-based web services?

Ans: The Uniform Resource Identifier (URI) is an acronym for Uniform Resource Locator. It's a string of characters used in the URI scheme to allow for unambiguous resource identification and extensibility.

A URI is used to find a resource(s) on the web service server.

Protocol:/service-name>/ResourceType>/ResourceID> is the format of a URI.

34. How do the PUT and POST methods differ?

Ans: There's a lot of confusion when it comes to using the PUT and POST methods. Our goal with a POST request is to create a new object on the server, whereas a PUT request replaces an existing object with another.

POST should be used when a client sends a page to the server, and the server then tells the client where it went. The PUT command should be used when the client specifies the page's location.

35. How should the API security be tested?

Ans: We must validate two things to test the API's security during API testing:

  • Authentication determines whether the end-identity user is correct.
  • The user's ability to use a resource is determined by authorization.
  • We can also check whether or not the TLS or SSL certificate used over the HTTPS protocol is valid.

36. How do you go about doing API load testing?

Ans: Load testing is a type of performance testing that examines an application's ability to perform under various user loads.

This is done to identify performance bottlenecks before the application goes live.

It's done by simulating many users hitting the API simultaneously, or in other words, artificial traffic, to see if the app can handle the load while maintaining consistency in response times and not affecting functionality.

JMeter is one such tool for performing load testing. Simulating artificial load on the AP3I allows you to create a test plan, define thread groups, and record test scripts. Finally, it includes a tool for visualizing the results of load testing. You can learn more about JMeter by visiting this page. 

37. Explain OAuth 2.0 Authentication

Ans: OAuth 2.0 authentication mechanism allows for secure API access without disclosing user credentials. In this procedure, a client (third-party software) asks permission to access a user's resource. The user is forwarded to an authorization server where their identity is verified and permission to share data is requested. An access token is given out if approved. The resource server accepts this token from the client, verifies it, and gives the user access to the requested material. OAuth 2.0, which is frequently used for user authentication and third-party app access, improves security by preventing credential disclosure.

38. Explain how to handle security testing for an API that requires authentication and authorization.

Ans: Examining APIs for vulnerabilities such as injection attacks, authorization bypass, and data exposure is part of security testing them. To make sure they function properly, test several authentication techniques (such OAuth and JWT). Examine role-based access control, run tests with various authorization levels, and confirm that users can't access unapproved resources. To find security vulnerabilities, use tools like OWASP ZAP.

39. What are the challenges of testing microservices-based APIs, and how can you overcome them?

Ans: Testing microservices APIs can be complex due to distributed nature. Challenges include service dependencies, data consistency, and integration testing. Use contract testing tools like Pact to validate interactions between microservices. Implement mocks and stubs for testing dependent services independently. Use Docker for consistent environments and continuous integration for robust testing pipelines.

40. What factors need to be taken into account while load testing a RESTful API?

To evaluate a RESTful API's performance, load testing entails simulating a large number of concurrent queries. Create scenarios with different request types and loads using tools like JMeter or Gatling. To locate bottlenecks and scale the API, think about factors like concurrency levels, request rates, and monitoring server metrics.
 

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Frequently Asked Questions

How do you explain API testing in an interview? 

The process of testing application programming interfaces (APIs) comprises evaluating their usability, dependability, and performance. It entails making calls to API endpoints and checking replies to make sure they comply with requirements and allow for efficient communication between software components.

What are basic interview questions API testing? 

Basic API testing interview questions cover topics like defining API testing and its importance, describing the many types of API tests (such unit, integration, and functional tests), differentiating API testing from UI testing, identifying popular HTTP methods, and going into detail about experience with API testing tools.

What are the 3 types of testing in API? 

There are three main forms of API testing: security testing, which identifies flaws and ensures data protection within the API, performance testing, which evaluates speed and scalability, and functional testing, which checks input/output and behaviour.

What are the 4 method API testing?

In API testing, four key techniques are applied. First, Unit Testing checks the accuracy of each individual function or method within the API. Second, integration testing examines how well various API components work together. Third, end-to-end testing measures how well the entire API workflow performs in practical situations. Fourth one, makes ensuring that any modifications or upgrades to the API do not adversely affect already-existing functionalities. 

What are the 4 methods of API testing?

The four main methods of API testing are:

  1. Unit Testing: Testing individual components or functions of the API in isolation.
  2. Functional Testing: Verifying the functionality of the API by testing its endpoints and responses.
  3. Load Testing: Assessing the API's performance under various levels of load and stress.
  4. Security Testing: Evaluating the API's security measures to ensure protection against vulnerabilities and unauthorized access.

What are the 5 HTTP methods?

The five common HTTP methods used in API requests are:

  1. GET: Retrieves data from the server.
  2. POST: Submits data to the server to create a new resource.
  3. PUT: Updates an existing resource on the server.
  4. DELETE: Removes a resource from the server.
  5. PATCH: Partially updates a resource on the server.

Conclusion

Candidates are frequently asked about what API testing is and how important it is to the software development lifecycle during API testing interviews. For freshers with little experience, the article discussed frequently asked API Testing interview questions, and knowing how to answer them will help you ace your job interviews with ease.

Recommended Read: Manual testing interview questions

We hope that this blog has helped you enhance your preparation for API Testing Interview questions and if you would like to learn more, visit coding ninjas studio.

Happy Coding!

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