Questions for API Testing Interviews

APIs are an essential part of the modern web because they enable developers to share data across multiple platforms.

You may be asked to test an API as a software tester. You will need to be able to both technical and non-technical to tackle this task. It is important to have a solid understanding of APIs and how they work.

This blog post will cover some of the most common questions and answers for Web API testing interviews. We’ll discuss them and provide some suggestions on other topics.

Let’s look at some questions every hiring manager will ask you during a Software Testing interview before we move on.

Let’s get to the point with the post API Interview Questions and Answers.

Interview Questions Web API Testing Best Practices

1. What is an API?

API stands for Application I nterface. API refers to a collection of protocols, routines and tools that can be used to build Software Applications. APIs define how a software program should interact.

API is Application PHrogramming interface. API is an interface that allows two software programs to communicate with one another. API refers to a set of software functions that can all be executed by another program.

2. What is API Testing?

API testing is a form of software test . It involves testing APIs both directly and as part of integration testing. This allows you to verify that the API meets your expectations regarding functionality, reliability, security, and performance. API Testing will focus on the Business logic layer in the software architecture. API testing can be done on any software system that contains multiple APIs.

3. What are the most common API Testing Types?

These are the most common practices for API testing:

  • Unit testing
  • Functional testing
  • Load testing
  • Runtime/ Error Detection
  • Security testing
  • Testing UI
  • Interoperability testing and WS Compliance testing
  • Testing for penetration
  • Fuzz testing

4. Name some common protocols that are used in API Testing.

These are some of the protocols used in API Testing:

What architectural styles are used to create Web APIs?

These are some of the architectural styles that can be used to create web api:

  • Simply use URI to identify the address of the service
  • Communication that is not stateless
  • HTTP is used for client-server communication
  • XML/JSON is a formatting language

What’s an API test environment?

API testing environments do not have a GUI (Graphical User Interface).

API’s test environment is a complex approach. It configures the database and server to meet the requirements of the software application. API will be tested for proper functioning after the installation is complete.

API calls are used to determine the parameters of the original environment and examine the test results.

5. What is the difference between API and web services?

Web Services:

1. All web services can be accessed via APIs
2. All web services must be accessible over the web (HTTP).
3. The three most common ways to use a Web service are SOAP, REST, and XML.
4. To be able to provide Web services, you need a network.


1. All APIs can be used to create web services.
2. All APIs do not need to be accessible over the web (i.e. HTTP)
3. API can communicate in multiple ways, e.g. DLL files in C/C++ and Jar files/ RMI for Java, Interrupts in Linux Kernel API, etc.
4. APIs do not require a network to operate

6. What is soap?

SOAP stands to represent Simple Object Access Protocol. It is an XML-based messaging protocol. It facilitates information exchange between computers.

7. What is Rest API?

REST stands to represent the Representational State Transfer. It is a collection of functions that developers can use to make requests and get responses. The HTTP Protocol in RESTAPI allows for interaction.

8. What is the difference between SOAP and REST?

1. SOAP allows two computers to communicate using XML documents.
2. SOAP only supports XML formats
3. SOAP doesn’t support caching
4. SOAP is slower that REST
5. SOAP acts as a custom desktop app, and is closely linked to the server.
6. SOAP works on HTTP, but it envelopes the message

1. REST is a service architecture design for network-based, software architecture.
2. REST supports different data formats
3. REST supports caching
4. REST is quicker than SOAP
5. REST client works just like a browser, but uses standard methods. An application must fit within it.
6. To hold meta information, REST uses HTTP headers

9. What are some common tests you can run on APIs?

These are some of the most common API tests that we do.

1. Verify that the return value is calculated based on the input condition. Based on the request, the APIs’ response should be checked.
2. When the API updates any data structure, verify that the system authenticates the outcome
3. Check if the API triggers another event.
4. If there is no return value, verify the API’s behavior

10. What are the benefits of API Testing?

  • API Testing is more efficient than GUI Testing. Because API testing automation is less code, it can offer faster and more thorough coverage.
  • API Testing can help us reduce testing costs. API Testing can detect minor bugs before GUI Testing. These bugs can become more serious during GUI Testing. The Company will save money by finding these bugs during API Testing.
  • API Testing does not require any language to be performed.
  • API Testing is a great tool for testing Core Functionality. The APIs can be tested without the need for a user interface. GUI Testing requires that we wait for the application to be available before testing the core functionality.
  • API Testing can help us reduce risks.

11. What is the most important thing to verify in API Testing?

API Testing basically involves sending an API request with known data to obtain a response.
1. Data accuracy
2. Status codes for HTTP
3. Response time
4. API error codes
5. Authorization checks
6. Non-functional testing like security testing and performance testing

12. Name some tools that are used to test APIs?

These are some of the tools that can be used to test APIs:

  • Katalon Studio
  • Assertible
  • Tricentis Tosca
  • Apigee
  • JMeter
  • Rest-Assured
  • Karate DSL
  • API Fortress
  • Parasoft
  • QTP(UFT),
  • vREST
  • Airborne
  • API Science
  • APIary Inspector
  • Citrus Framework
  • Hippie-Swagger

13. What are the most popular templates for API documentation?

These are some of the API documentation templates.

  • Swagger
  • FlatDoc
  • RestDoc
  • API blueprint
  • Slate
  • Miredot
  • Specification of web service API.

14. Name some API examples that are very popular.

Here are some of the most popular API examples

  • Google Maps API
  • YouTube
  • Twitter
  • Amazon Advertising API

15. What is the difference between Unit Testing and API Testing?


  • The Development Team conducts unit testing
  • Unit testing is a type of White Box testing
  • Before including code into a build, unit testing is done.
  • Unit testing involves the use of source code
  • Unit testing has a limited scope, therefore, only the most basic functions are tested.


  • The QA Team conducts API testing
  • API testing is a type of Black box testing
  • After the build is available for testing, API testing takes place.
  • API testing does not require the use of source code
  • API testing has a broad scope, which means that all functional issues can be tested.

16. What are the biggest challenges in API testing?

Here are some of the problems we encounter while API testing

  • Selection of the right parameters and their combinations
  • Identify the parameters correctly
  • Proper call sequencing is essential as it may result in inadequate coverage during testing
  • Validating and verifying the output
  • It is difficult to input values because there is no GUI

17. What bugs can we expect to encounter when testing APIs?

Observations made during API testing

  • Security, stress, and performance issues
  • Duplicate functionality or it is missing
  • Reliability problems
  • Improper messaging
  • Incompatible error handling mechanism
  • Multi-threaded issues
  • Improper errors

18. What is the difference between UI and API testing?

The UI (User Interface), testing is used to verify the graphical interface portion of an application. Its primary focus is to check the appearance and feel of an app. API testing allows communication between two software systems. It focuses on the business layer of an application.

19. Name the most popular HTTP methods.

Some HTTP methods can be used to send data.

GET This allows you to retrieve data from a Server
POST This allows you to add data or resources to an existing file in a server
PUT This allows you to replace an existing resource or file in a server
DELETE This allows you to delete data from a server
PATCH This is used to make partial modifications to a resource
OPTIONS This is used to describe communication options for the target resource
HEAD This request asks for a response that is identical to a GET request but without the body.

20. You can use GET request to create a resource instead of PUT.

No, GET request allows only read-only rights. You can retrieve data from a server, but it does not create a resource. To create a resource, you should use the PUT or POST method.

21. What’s the difference between PUT methods and POST?

Sometimes PUT and Post methods can be confused about when they should be used. With POST request, we are requesting to create a new object, whereas with PUT, we are requesting to replace an existing object.

When the client sends the page, POST should be used. The server will then let the client know where it was placed. PUT should only be used when the client specifies where the page is located.

This concludes the post “API Testing Interview Questions”. For future reference, please bookmark this post “API Interview Question and Answers”.

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