Top 50 API Testing Interview Questions and Answers for Freshers & Experienced

Introduction

Congratulations! That long-awaited email is here. An email regarding your job interview for an API tester. 

So, you are here looking for the most common API testing interview questions. You are doing the right thing. It is always recommended to prepare for these frequently asked questions before an interview. And we understand the importance of it. 

API (Application Programming Interface) testing is considered the future of software testing because of its endless advantages, time effectiveness, language independence, or GUI (Graphical User Interface) integration, etc. Today, API testing has become a must-have requirement for all software testing projects to ensure maximum product quality.

Whether you are a fresher or experienced, we have prepared these most frequently asked API testing interview questions taking reference from actual interviews to help you ace your next interview.

A. API Testing Interview Questions and Answers For Freshers

Here are the basic interview questions on API testing that you must start with.

Q1. What is an API?

Ans:- This is the most basic and crucial question among the API testing interview questions

 API (Application Programming Interface) is a software intermediary that helps communication and data exchange between two software systems.

You can also give more information about the API examples such as Google Maps API, Youtube API, Twitter API, AmazonAdvertising API,  and if you have previously worked on any.

Q2. What is API testing?

This question is mostly asked question among the API interview questions to check if you can efficiently frame your answer. 

Ans: API testing is the testing of the developed so APIs to check their functionality, efficiency, reliability, and security. 

You can mention types of API testing such as 

• Validation testing
• Functional testing
•  load testing
• UI testing
• Run time/error detection
• penetration testing
• Fuzz testing
• Interoperability and WS Compliance testing.

Q3. What are the advantages of API Testing?

Give this answer in a way to show the interviewer the importance and relevance of API testing and where and how you are going to use it or have already used it. 

Ans:-

• API testing helps in core functionality by giving direct access to the application, without needing a user interface. It is helpful in detecting minor errors before they turn into major issues during GUI testing.
• API testing uses less code than GUI testing so it gives better coverage. That’s hat it is time-effective too.
• API testing is language-independent as data is exchanged using XML or JSON, which allows users to select any coding language when adopting an automation test service.
• API can be easily integrated with GUI testing.

Q4. How does API work?

Ans:- Generally, API takes a request, processes it which is data validation, database interaction, data processing, and then the result is reverted to the source. 

Q5.  Do you know about the common tests performed on the APIs?

Ans:-Here is the list of common tests that are performed on APIs –

• You should verify the API first and check whether it is updating any data structure or not.
• You need to check whether the API returns anything.
• As per the given parameters or values, the values returned by APIs need to be checked.
• Verify the API whether it triggers any other event or calls another API.

Q6. What are the protocols used in API testing?

Ans:-These are the protocols used in API testing:

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

Q7. What are the most commonly used tools in API testing?

Ans:-There are numerous API testing tools available. Some of the tools are Postman, Katalon studio, SoapUi, Apigee, JMeter, Parasoft SOAtest, Apigee, API fortress, JUnit, etc.

Q8.  What to perform API test?

• Select the suite where you will add the API test case that you are going to test
• Select the test development mode
• Create test cases for desired API methods
• Configure control parameters, test conditions, and validation method
• Perform API test
• View and analyze test reports
• Filter and sequence API test cases

 Q9. What should you take care of while writing cases?

Ans:-These are the points you can reply with

• The test cases need to e aligned with the end-user interest.
• The steps should be simple so that anyone can use them later.
• Make sure that the test cases are reusable.
• Define the importance of the test cases.
• Provide a valid description, test input parameters, test data, expected outcome after.
• running so that the comparison can be done with the estimated one.
• Test cases should include negative test scenarios too.
• Naming conventions need to be strictly followed while creating the test cases.
• Check for updates daily.

Q10. What needs to be verified in API testing?

Ans:-In API Testing, we usually send a request to the API, and then we analyze the responses keeping the following parameters in mind:

• Comparing the actual response with the expected response to get data accuracy.
• HTTP status codes of the produced API.
• Response time of the API.
• Error codes if the APIs if there are errors
• Authorization Details
• Test for security, performance, availability, etc

 Q11. Define Test Data.

Ans:- Test data is the input data used to perform test cases. This data can be prepared either manually or by using different tools. For example, to test the login functionality of an application, the input data will be username and password which constitutes the test data.

Q12. Define test coverage.

Ans:- Test coverage amount of testing performed by making use of test cases. It can be either functional testing or non-functional testing.

Q13. What is a SOAP web service?

Ans:- SOAP means Simple Object Access Control Protocol and this is an XML-based protocol that is used to exchange information between computer machines.

Q14. What do you understand about the REST API?

Ans:- Rest ( REpresentational State Transfer) API is defined as the set of functions that helps a developer in sending requests and receiving responses. In this protocol, the interaction is always made through an HTTP protocol. The meaning of REST is Representable State Transfer that has become a defacto standard for API creation these days.

Q15. How will you differentiate the API testing and the UI testing from each other?

Ans:- UI or User-Interface testing is used to check the graphical interface of an application or software program, how the user interacts and reacts to different elements like fonts, images, layouts, etc. This testing is majorly focused on the look and feel of an application.

At the same time, API enables communication among two different software components. Any software system implementing an API contains functions or subroutines that can be executed by any other software system.

Q16.  How will you differentiate between API Testing and Unit Testing?

Api Testing	Unit Testing
Performed by QA team	Performed by the development team
This is a form of black-box testing	This is a form of White box testing
Full functionality of the software is checked as it will be used by external developers (The end-user)	Here each unit is tested for functionality.If each unit is performing well in isolation.
The tester usually does not have the access to the source code, only the functionality test is done.	The developer has the access to the unit test cases as they test these before they proceed for the next step.

Q17. What is test documentation?

Ans:-The API documentation is technical writing giving instructions on how to use and integrate with an API efficiently. It gives reference to the information needed to work with the API and helps you get API testing questions.

Q18. When you are writing an API document, what are the major areas to focus on?

Ans:-Here is the list of major areas that you should focus on while writing an API document –

• Focus on the content source
• Sketch or document the plan well.
• Layout delivery
• Detailed information about each of the functions
• Automatic document creation programs

Q19.  For any API document, how can we document different functions?

Ans:-Syntax – Here, you have to write the syntax for the parameter of the code in the same sequence as they occur, highlight necessary elements, optional elements, etc.

• Description – Give a quick description of each of the functions
• Error Messages – Here you need to give the syntax of error messages.
• Parameters – Give proper details about function parameters.
• Related Links – Connection fields
• Example Code – A small snippet of the code

Q20.  Mention the list of tools that are needed for the documentation.

Ans:-Read: Automation Testing Tutorial Guide for Beginner

For Java Code, you can use JavaDoc and for the .Net code, you can use Doxygen.

Q21. Difference between API and Web services?

Ans:-

API	Web Services
All APIs are not web services	All web services are APIs
All APIs need not be exposed over the web(i.e. HTTP)	All web services need to be exposed over the web(HTTP)
API uses multiple ways for communication e.g. DLL files in C/C++, Jar files/ RMI in java, Interrupts in Linux kernel API, etc	A Web service uses only three styles of use: REST, SOAP, and XML-RPC for communication
A Web services are network dependent	APIs don’t need a network for operation

As you are now aware of the API interview questions asked for freshers, Now let’s move towards the advanced API interview questions. Get prepared for all the API interview questions, You never know.

B. Advanced API Testing Interview Questions and Answers

Here are the API interview questions that should you prepare while appearing for the senior profiles. These API testing interview questions are asked mostly to test your knowledge and experience, so try to flaunt your experience here to impress the interviewer.

Q22. What is the basic process to test an API? Explain based on your previous experiences.

Ans:- Here are the basic steps to follow to test an API –

• First of all, decide the suite where you wanted to add the API test case.
• Now select the test development code too.
• Now you have to develop test cases for needed API methods.
• This is the time to configure the app control parameters.
• Configure the test conditions too.
• Validate the methods and configure them
• Execute APIs, check the test reports, filter the test cases, arrange the test cases etc.

By following these steps in the same sequence as given, this is easy to test an API successfully.

Q23. What are the errors expected during API testing?

Ans:-These are the errors you can tell to let them know that you have performed such tests before and you know what you claim.

• Security
• Duplicate or missing functionality
• stress
• Reliability
• Unused flags
• Performance
• Incompatible error handling
• Multi-threatening
• Improper errors

Q24. What are the major challenges faced while performing API testing?

Ans:- This is one of the most asked API testing interview questions.

You can always talk about the challenges you perform while doing API testing, or the list can go like this.  

• Initial setup
• parameter selection
• combination and validation
• sequencing the API calls
• Updating the schema
• tracking system integration.

Q25. What is the test environment of API?

Ans:- Setting up an API environment is not easy, so try to share your experience and try to communicate with the interviewer on this.

The test environment of API is a bit complete and requires the configuration of both database and server is done without the integration of GUI.

After installation, API is verified for the right operation. Throughout the process, we study the test process by setting up the API with different parameters. 

Q26. What are the principles of an API test design?

Ans:- It is one of the API design interview questions. You can answer it like this:

 The seven principles of API test design are listed below.

• Exhaustive testing is not possible. In fact, we need to do an optimal amount of testing which relies on the risk assessment of the application.
• Defect Clustering states that a small number of modules carries most of the errors. In 20% of the module, approximately 80% of defects are found. Finding such defects depends on experience.
• You should not conduct the same set of repetitive tests, The same method will not be sufficient to recognize new defects. A metaphor here is the pesticide paradox. Usage of the same pesticide over and over will lead to the evolution of the insects and they will soon become resistant to the pest. The same applies here.
• The absence of defects needs to be taken care of. The testing principle states that the tests inform about the presence of defects not about the absence of a defect. So, even if no defects are found, it can’t be proof of correctness.
• The absence of defect is a fallacy. Sometimes, the software which is 99% bug-free is still not usable. This can happen if the system is tested for the wrong requirements. So, finding errors and correcting them will not help if the requirements of the end-user are not taken care of.
• Early testing is always helpful, if the error is solved in the requirement or design phase, it is easier and cheaper. So, we should start testing in the early stages of the development life-cycle.
• Testing is context-dependent. All the developed software is not identical. You need to test all software based on the context. You might use different approaches, techniques, methodologies, and types of tests for different software and requirement. A POS system will be different for a retail store and an ATM machine.

Q27. What do you understand by Black Box Testing?

Ans:- Black Box Testing is a method of software testing where the testers evaluate the functionality of the application without peering into the internal source code. This method can be applied in every level of software testing such as integration testing, unit testing, system testing, 

and acceptance testing.

 

Q28.  What do you understand about the API Framework?

Ans:- There is no need to give an introduction to the API Framework as it is self-explanatory. When you are testing APIs then you don’t have to work on each API independently but you can use config files in that case where details for all APIs are given and can be used if needed.

 Q29. Explain the working of API builders.

Ans:- API builder is a PL SQL program that is made up of four SQL files where one file is responsible for starting the process, two files are used to create the temp tables or the master package, and the fourth file will help in generating the final output.

Q30. What is a Test API?

Ans:- Test API is a set of test APIs or a library of utility that helps developers or testers in creating testing tools and automated test cases for .Net or WIN 32 applications. It also offers a set of basic building blocks, data structures, data types, algorithms, etc.

Q31How do you test the API security?

Ans:- For testing the security of API during API testing, we need to validate 2 things:

• Authentication: Whether the identity of the end-user is correct.

• Authorization: Whether the user has access to the resource.

We can also check whether the TLS or the SSL certificate used over the HTTPS protocol is valid or not.

Q32. What are the different types of Input Injection and what are the different ways of stimulating user input?

Ans:- Input injection is a popular act of simulating user inputs and it can be done in popular ways as listed below –

Read: What is Unit Testing? Unit Testing Tutorial Guide for Beginners

• By direct method invocation
• With the help of an accessibility interface
• By simulating low-level input
• By simulating a device driver
• Simulation using a robot

Q33. How to perform the API testing with Run Scope?

Ans:- Run Scope is a web application that supports backend services and easy to understanding user interface tool for testing APIs.

Q34.  What are the different principles of API testing design?

Ans:- The major principles include – Setup, Execution, Verification, Reporting, Clean up, etc.

Q35. What are the tools that should be used for API test automation?

Ans:- The automation tools that are frequently used for API test automation include – JUnit for Java, SOAP UI, HP UFT, or NUnit for .NET, etc.

Q36. What is caching and how does it work?

Ans:- Caching is a mechanism to improve the performance of applications. It is a process of storing and accessing data from a cache. A cache can be defined as a software or hardware component intended at storing data so that future requests for the same data can be retrieved faster.

e XML, like the SMTP server or POP3 protocol to pass the messages or reply to queries.

Q37. Name some commonly used  API documentation templates?

Ans:- There are numerous API documentation templates available to make the entire process simple and straightforward.

• Slate
• Miredot
• Swagger
• FlatDoc
• API blueprint
• RestDoc
• API doc
• Web service API specification

Get a complete PDF of API Testing interview questions here!

C. Commonly Asked Rest Assured Interview Questions And Answers

These are 7 rest assured API automation testing interview questions and answers to give you a knowledge of REST assured, RESTful web services, URI, and the types of HTTP methods. You can face such API questions too.

 Q38. What is REST assured?

Ans:- REST Assured is a Java-based library that is used for RESTful APIs testing. It can be used to test applications based on JSON and XML. Also, all methods are entirely supported, including PUT, POST, GET, PATCH, and DELETE.

 Q39. What are RESTful web services?

Ans:- Restful web services are REST Architecture-based Web services. RESTful web services use HTTP as a communication between the server and the client.

 Q40. What is URI?

Ans:- URI (Uniform Resource Identifier) consists of the base URL, path parameter, and query parameter.

 Q41.  Which HTTP methods are used in REST and what do they do?

Ans:- You definitely should remember these HTTP methods before going to appear API testing interview questions.

• GET: Retrieves resource representation. Should be cacheable.
• POST: Creates a new subordinate resource. Not cacheable
• PUT: Updates existing resources. If the resource does not exist, then API may decide whether to create a new one or not.
• PATCH: Makes a partial update
• DELETE Deletes the resource. Idempotent and not cacheable
• OPTIONS: Describe the communication options for the target resource.
• HEAD: Asks for a response identical to that of a GET request, but without the response body.

Q42. Can You explain the payload?

Ans. Payload/body is highly secured input data that is sent to API to process the request. The payload is usually in JSON format in REST API.

Q43. What is the difference between PUT and POST? 

Ans. The main difference between PUT and POST is PUT requests are idempotent. Calling the same PUT request multiple times will always respond with the same result. In contrast, calling a POST request repeatedly have the side effects of creating the same resource multiple times.

Q44. can we use GET request instead of PUT to create a resource?

Ans. PUT and POST method is used to create a resource. GET is only used to request the resources.

D. Frequently Asked SOAP Interview Questions and Answers

Get the Knowledge of SOAP to be able to answer any SOAP-related questions swiftly.

Q45. What are SOAP Web services?

Ans:- This is one of the fundamental API testing interview questions that you must know the answer to.

The SOAP (Simple Object Access Protocol) is defined as an XML-based method used in web services.  It is both platform and language independent.

It is well known for designing and developing web services. It also enables the communication between applications developed on different platforms using various programming languages over the Internet.

Q46.How does SOAP work?

Ans:- SOAP provides a user interface that can be accessed by the client’s server object, and the request sent by it goes to the server, which can be accessed using the server object. The user interface creates some files or methods consisting of server objects and the name of the interface to the server object.

 It also contains other information such as the name of the interface and methods. It uses HTTP to send the XML to the server using the POST method, which analyzes the method and sends the result to the client. 

The server creates more XML consisting of responses to the request of the user interface using HTTP. The client can use any approach to send the XML, like the SMTP server or POP3 protocol to pass the messages or reply to queries.

Q47.What are the syntax rules for a SOAP message?

Ans:- These are some basic syntax rules for an SAOP message

• Must use encoded XML
• Envelope namespace must be used
• Encoding namespace must be used
• Must not consist of a DTD reference
• Must not have XML processing instruction

Q48.How do users utilize the facilities provided by SOAP?

Ans:-

• PutAddress(): we use it to enter an address in the webpage and has an address instance on the SOAP call.
• PutListing(): It is utilized to allow the insertion of a complete XML document into the web page. It receives the XML file as an argument and transports the XML file to XML parser liaison, which reads it and inserts it into the SOAP call as a parameter.
• GetAddress(): It helps in getting a query name and getting the result that best matches a query. The name is sent to the SOAP call in the form of the text character string.
• GetAllListing(): It helps to return the full list in an XML format

Q49. Tell the elements of SOAP message structure

Ans:- It is an ordinary XML document that contains the elements as a SOAP message

• Envelope: It is a mandatory root element that translates the XML document and defines the start and end of the message
• Header: It is an optional element. It stores the information about the message being sent
• Body: It contains the XML data comprising the message being sent
• Fault: It informs about the errors that occurred while processing the message

 Q50. What are the obstacles users face while using SOAP?

Ans:- The major difficulty faced by users using SOAP is a firewall security mechanism. This locks all the ports leaving some like HTTP port 80 used by SOAP that bypasses the firewall. 

The major technical issue with SAOP is, it mixes specifications of message transport and message structure.

The Final Solution To Face API Testing Interview Questions

The above-mentioned advanced API testing interview questions and answers will be very helpful for you when an interviewer will focus on finding out the functional knowledge of the domain.

These API testing interview questions have been extracted from real-time interviews, and are found to be mostly asked. So, better prepare them with sheer dedication, attention, and confidence. 

For cracking these API testing interview questions, you should have practical knowledge when working with any technology and to help you get that, enroll in our automation testing training online.

Read: What is JIRA? JIRA Tutorial Guide for Beginner

If you have any queries on these interview questions on API testing, feel free to contact us via commenting down below or hitting our free career counseling!

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