API Interview Questions

What is the caching mechanism?

Caching is just the practice of storing data in temporarily and retrieving data from a high-performance store (usually memory) either explicitly or implicitly. When a caching mechanism is in place, it helps improve delivery speed by storing a copy of the asset you requested and later accessing the cached copy instead of the original.

What is the procedure to perform API testing?

Choose the suite to add the API test case Choose the test development mode Demand the development of test cases for the required API methods Configure the control parameters of the application and then test conditions Configure method validation Execute the API test Check test reports and filter API test cases Arrange all API test cases

What are the different types of IoC (dependency injection)?

Constructor-based dependency injection − Constructor-based DI is accomplished when the container invokes a class constructor with a number of arguments, each representing a dependency on other class. Setter-based dependency injection − Setter-based DI is accomplished by the container calling setter methods on your beans after invoking a no-argument constructor or no-argument static factory method to instantiate your bean.

What must be checked when performing API testing?

During the API testing process, a request is raised to the API with the known data. This way you can analyze the validation response. While testing an API, you should consider: Accuracy of data Schema validation HTTP status codes Data type, validations, order and completeness Authorization checks Implementation of response timeout Error codes in case API returns, and Non-functional testing like performance and security testing

What are benefits of using spring?

Following is the list of few of the great benefits of using Spring Framework: Lightweight − Spring is lightweight when it comes to size and transparency. The basic version of spring framework is around 2MB. Inversion of control (IOC) − Loose coupling is achieved in spring using the technique Inversion of Control. The objects give their dependencies instead of creating or looking for dependent objects. Aspect oriented (AOP) − Spring supports Aspect oriented programming and enables cohesive development by separating application business logic from system services. Container − Spring contains and manages the life cycle and configuration of application objects. MVC Framework − Spring's web framework is a well-designed web MVC framework, which provides a great alternative to web frameworks such as Struts or other over engineered or less popular web frameworks. Transaction Management − Spring provides a consistent transaction management interface that can scale down to a local transaction (using a single database, for example) and scale up to global transactions (using JTA, for example). Exception Handling − Spring provides a convenient API to translate technology-specific exceptions (thrown by JDBC, Hibernate, or JDO, for example) into consistent, unchecked exceptions.

What are the most commonly used HTTP methods supported by REST?

GET is only used to request data from a specified resource. Get requests can be cached and bookmarked. It remains in the browser history and haS length restrictions. GET requests should never be used when dealing with sensitive data. POST is used to send data to a server to create/update a resource. POST requests are never cached and bookmarked and do not remain in the browser history. PUT replaces all current representations of the target resource with the request payload. DELETE removes the specified resource. OPTIONS is used to 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.

What are the factors that help to decide which style of Web services - SOAP or REST - to use?

Generally, REST is preferred due to its simplicity, performance, scalability, and support for multiple data formats. However, SOAP is favorable to use where service requires an advanced level of security and transactional reliability. But you can read the following facts before opting for any of the styles. Does the service expose data or business logic? REST is commonly used for exposing data while SOAP for logic. The requirement from clients or providers for a formal contract. SOAP can provide contract via WSDL. Support multiple data formats. Support for AJAX calls. REST can apply the XMLHttpRequest. Synchronous and asynchronous calls. SOAP enables both synchronous/ asynchronous operations whereas REST has built-in support for synchronous. Stateless or Stateful calls. REST is suited for stateless operations. Security. SOAP provides a high level of security. Transaction support. SOAP is good at transaction management. Limited bandwidth. SOAP has a lot of overhead when sending/receiving packets since it's XML based, requires a SOAP header. However, REST requires less bandwidth to send requests to the server. Its messages are mostly built using JSON. Ease of use. REST based application is easy to implement, test, and maintain.

What is Dependency Injection?

Inversion of Control (IoC) is a general concept, and it can be expressed in many different ways and Dependency Injection is merely one concrete example of Inversion of Control. This concept says that you do not create your objects but describe how they should be created. You don't directly connect your components and services together in code but describe which services are needed by which components in a configuration file. A container (the IOC container) is then responsible for hooking it all up.

What are the elements of a SOAP message structure?

It is a common XML document that contains the elements as a SOAP message Envelope: It is an obligatory root element that translates the XML document and defines the beginning and end of the message. Header: It is an optional item which contains information about the message being sent. Body: It contains the XML data comprising the message being sent. Fault: It provides the information on errors that occurred while during message processing.

What is Spring Java Based Configuration? Give some annotation example.

Java based configuration option enables you to write most of your Spring configuration without XML but with the help of few Java-based annotations. For example: Annotation @Configuration indicates that the class can be used by the Spring IoC container as a source of bean definitions. The @Bean annotation tells Spring that a method annotated with @Bean will return an object that should be registered as a bean in the Spring application context.

What are some key characteristics of REST?

Key characteristics of REST are likely asked in a Web API Testing interview. So please get the answer ready in your mind with these 2 ones: REST is stateless, therefore the SERVER has no status (or session data) With a well-applied REST API, the server could be restarted between two calls, since all data is transferred to the server Web service uses POST method primarily to perform operations, while REST uses GET for accessing resources.

What are the Limits of API Usage?

Many APIs have a certain limit set up by the provider. Thus, try to estimate your usage and understand how that will impact the overall cost of the offering. Whether this will be a problem depends in large part on how data is leveraged. Getting caught by a quota and effectively cut-off because of budget limitations will render the service (and any system or process depending on it) virtually useless.

Some common protocols used in API testing?

Many protocols are now available to be used in API testing, such as JMS, REST, HTTP, UDDI and SOAP.

What is a RESTFul Web Services?

Mostly, there are two kinds of Web Services which should be remembered in your next API testing interview: SOAP (Simple Object Access Protocol) - an XML-based method to expose web services. Web services developed in the REST style are referred to as RESTful web services. These web services use HTTP methods to implement the concept of REST architecture. A RESTful web service usually defines a URI, Uniform Resource Identifier a service, provides resource representation like JSON and a set of HTTP methods.

What are the syntax rules for a SOAP 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

Is there any difference between PUT and POST operations?

PUT and POST operation are quite similar, except the terms of the result generated by them. PUT operation is idempotent, so you can cache the response while the responses to POST operation are not cacheable, and if you retry the request N times, you will end up having N resources with N different URIs created on server. In a Web API Testing interview, you should give a specific example for PUT and POST operations to make crystal clear to the interviewer.

How users utilize the facilities provided by SOAP?

PutAddress(): It is used to enter an address in the webpage and has an address instance on the SOAP call. PutListing(): It is used 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 is used to get a query name and gets the result that best matches a query. The name is sent to the SOAP call in the form of text character string. GetAllListing(): It is used to return the full list in an XML format.

What is REST?

REST (Representational State Transfer) is an architectural style for developing web services which exploit the ubiquity of HTTP protocol and uses HTTP method to define actions. It revolves around resource where every component being a resource that can be accessed through a shared interface using standard HTTP methods. In REST architecture, a REST Server provides access to resources and REST client accesses and makes these resources available. Here, each resource is identified by URIs or global IDs, and REST uses multiple ways to represent a resource, such as text, JSON, and XML. XML and JSON are nowadays the most popular representations of resources.

What is a "Resource" in REST?

REST architecture treats any content as a resource, which can be either text files, HTML pages, images, videos or dynamic business information. REST Server gives access to resources and modifies them, where each resource is identified by URIs/ global IDs.

What is the most popular way to represent a resource in REST?

REST uses different representations to define a resource like text, JSON, and XML. XML and JSON are the most popular representations of resources.

What is messaging in RESTful Web services?

RESTful web services use the HTTP protocol as a communication tool between the client and the server. The technique that when the client sends a message in the form of an HTTP Request, the server sends back the HTTP reply is called Messaging. These messages comprise message data and metadata, that is, information on the message itself.

Which protocol is used by RESTful Web services?

RESTful web services use the HTTP protocol as a medium of communication between the client and the server.

SOAP or Rest APIs, which method to use?

SOAP is the heavyweight choice for Web service access. It provides the following advantages when compared to REST: SOAP is not very easy to implement and requires more bandwidth and resources. SOAP message request is processed slower as compared to REST and it does not use web caching mechanism. WS-Security: While SOAP supports SSL (just like REST) it also supports WS-Security which adds some enterprise security features. WS-AtomicTransaction: Need ACID Transactions over a service, you're going to need SOAP. WS-ReliableMessaging: If your application needs Asynchronous processing and a guaranteed level of reliability and security. Rest doesn't have a standard messaging system and expects clients to deal with communication failures by retrying. If the security is a major concern and the resources are not limited then we should use SOAP web services. Like if we are creating a web service for payment gateways, financial and telecommunication related work, then we should go with SOAP as here high security is needed. REST is easier to use for the most part and is more flexible. It has the following advantages when compared to SOAP: Since REST uses standard HTTP, it is much simpler. REST is easier to implement, requires less bandwidth and resources. REST permits many different data formats whereas SOAP only permits XML. REST allows better support for browser clients due to its support for JSON. REST has better performance and scalability. REST reads can be cached, SOAP based reads cannot be cached. If security is not a major concern and we have limited resources. Or we want to create an API that will be easily used by other developers publicly then we should go with REST. If we need Stateless CRUD operations then go with REST. REST is commonly used in social media, web chat, mobile services and Public APIs like Google Maps. RESTful service returns various MediaTypes for the same resource, depending on the request header parameter "Accept" as application/xml or application/json for POST and /user/1234.json or GET /user/1234.xml for GET. REST services are meant to be called by the client-side application and not the end user directly. ST in REST comes from State Transfer. You transfer the state around instead of having the server store it, this makes REST services scalable.

How does SOAP work?

SOAP is used to provide a user interface that can be accessed by the client object, and the request that it sends goes to the server, which can be accessed using the server object. The user interface creates some files or methods consisting of server object 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 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.

What is the test environment of API?

Setting up the API's test environment is not an easy task, so you should have a ready answer if your API testing interview is coming. The test environment of API is a bit complete and requires the configuration of the database and server, depending on the software requirements. No GUI (Graphical User Interface) is available in this test form. When the installation process is complete, API is verified for the proper operation. Throughout the process, the API called from the original environment is set up with different parameters to study the test results.

Which DI would you suggest Constructor-based or setter-based DI?

Since you can mix both, Constructor- and Setter-based DI, it is a good rule of thumb to use constructor arguments for mandatory dependencies and setters for optional dependencies. Note that the use of a @Required annotation on a setter can be used to make setters required dependencies.

What is Spring configuration file?

Spring configuration file is an XML file. This file contains the classes information and describes how these classes are configured and introduced to each other.

What is Spring?

Spring is an open source development framework for enterprise Java. The core features of the Spring Framework can be used in developing any Java application, but there are extensions for building web applications on top of the Java EE platform. Spring framework targets to make J2EE development easier to use and promote good programming practice by enabling a POJO-based programming model.

How can you inject Java Collection in Spring?

Spring offers four types of collection configuration elements which are as follows − <list> − This helps in wiring i.e. injecting a list of values, allowing duplicates. <set> − This helps in wiring a set of values but without any duplicates. <map> − This can be used to inject a collection of name-value pairs where name and value can be of any type. <props> − This can be used to inject a collection of name-value pairs where the name and value are both Strings.

What are the advantages of API Testing?

Test for Core Functionality: API testing provides access to the application without a user interface. The core and code-level of functionalities of the application will be tested and evaluated early before the GUI tests. This will help detect the minor issues which can become bigger during the GUI testing. Time Effective: API testing usually is less time consuming than functional GUI testing. The web elements in GUI testing must be polled, which makes the testing process slower. Particularly, API test automation requires less code so it can provide better and faster test coverage compared to GUI test automation. These will result in the cost saving for the testing project. Language-Independent: In API testing, data is exchanged using XML or JSON. These transfer modes are completely language-independent, allowing users to select any code language when adopting automation testing services for the project. Easy Integration with GUI: API tests enable highly integrable tests, which is particularly useful if you want to perform functional GUI tests after API testing. For instance, simple integration would allow new user accounts to be created within the application before a GUI test started.

What is payload in RESTFul Web services?

The "payload" is the data you are interested in transporting. This is differentiated from the things that wrap the data for transport like the HTTP/S Request/Response headers, authentication, etc.

What is API documentation?

The API documentation is a complete, accurate technical writing giving instructions on how to effectively use and integrate with an API. It is a compact reference manual that has all the information needed to work with the API, and helps you answer all the API testing questions with details on functions, classes, return types, arguments, and also examples and tutorials.

Which purpose does the OPTIONS method serve for the RESTful Web services?

The OPTIONS Method lists down all the operations of a web service supports. It creates read-only requests to the server.

What is bean auto wiring?

The Spring container is able to autowire relationships between collaborating beans. This means that it is possible to automatically let Spring resolve collaborators (other beans) for your bean by inspecting the contents of the BeanFactory without using <constructor-arg> and <property> elements.

What are principles of an API test design?

The five most important principles of an API test design are: Setup: Create objects, start services, initialize data, etc Execution: Steps to apply API or the scenario, including logging Verification: Oracles to evaluate the result of the execution Reporting: Pass, failed or blocked Clean up: Pre-test state

What is the best approach method to perform API testing?

The following factors should be considered when performing API testing: Defining the correct input parameters Verifying the calls of the mixture of two or more added value parameters Defining the basic functionality and scope of the API program Writing appropriate API test cases and making use of testing techniques such as equivalence class, boundary value, etc. to check the operability Testing case execution Comparing the test result with the expected result Verifying the API behavior under conditions such as connection to files and so on.

What are Spring beans?

The objects that form the backbone of your application and that are managed by the Spring IoC container are called beans. A bean is an object that is instantiated, assembled, and otherwise managed by a Spring IoC container. These beans are created with the configuration metadata that you supply to the container, for example, in the form of XML <bean/> definitions.

How do you provide configuration metadata to the Spring Container?

There are following three important methods to provide configuration metadata to the Spring Container − XML based configuration file. Annotation-based configuration Java-based configuration

What are tools could be used for API testing?

There are myriad of different API testing tools available. A few of common tools are Katalon Studio, Postman, SoapUi Pro, Tricentis Tosca, Apigee, etc. While doing Unit and API testing, both targets source code. If an API method uses code based in .NET then another supporting tool must have .NET.

What are API documentation templates that are commonly used?

There are several available API documentation templates help to make the entire process simple and straightforward, which could be answered in your API testing interview, such as: Swagger Miredot Slate FlatDoc API blueprint RestDoc Web service API specification

What are the various approaches available for developing SOAP based web services?

There are two different methods available for developing SOAP-based web services, which are explained below: Contract-first approach: the contract is first defined by XML and WSDL, and then Java classes are derived from the contract. Contract-last approach: Java classes are first defined, and then the contract is generated, which is normally the WSDL file from the Java class. "Contract-first" method is the most popular approach.

What are types of IoC containers? Explain them.

There are two types of IoC containers − Bean Factory container − This is the simplest container providing basic support for DI .The BeanFactory is usually preferred where the resources are limited like mobile devices or applet based applications Spring ApplicationContext Container − This container adds more enterprise-specific functionality such as the ability to resolve textual messages from a properties file and the ability to publish application events to interested event listeners.

What does @Autowired annotation mean?

This annotation provides more fine-grained control over where and how autowiring should be accomplished. The @Autowired annotation can be used to autowire bean on the setter method just like @Required annotation, constructor, a property or methods with arbitrary names and/or multiple arguments.

What are some architectural styles for creating a Web API?

This is one of the fundamental Web API interview questions. Bellows are four common Web API architectural styles: HTTP for client-server communication XML/JSON as formatting language Simple URI as the address for the services Stateless communication

What are SOAP Web services?

This is one of the fundamental Web services testing questions that you must know the answer. The SOAP (Simple Object Access Protocol) is defined as an XML-based protocol. It is known for designing and developing web services as well as enabling communication between applications developed on different platforms using various programming languages over the Internet. It is both platform and language independent.

What is the difference between top down & bottom up approach in SOAP Web services?

Top down SOAP Web services include creating WSDL document to create a contract between the web service and the client, with a required code as an option. This is also known as Contract-first approach. The top-down approach is difficult to implement because classes must be written to confirm the contract defined in WSDL. One of the benefits of this method is that both client and server code can be written in parallel. Bottom up SOAP web services require the code to be written first and then WSDL is generated. It is also known as Contract-last approach. Since WSDL is created based on the code, bottom-up approach is easy to implement and client codes must wait for WSDL from the server side to start working.

What is URI? What is the main purpose of REST-based web services and what is its format?

URI stands for Uniform Resource Identifier. It is a string of characters designed for unambiguous identification of resources and extensibility via the URI scheme. The purpose of a URI is to locate a resource(s) on the server hosting of the web service. A URI's format is <protocol>://<service-name>/<ResourceType>/<ResourceID>.

When to use SOAP API?

Use the SOAP API to create, retrieve, update or delete records, like accounts, leads, and user-defined objects. With more than 20 different calls, you can also use the SOAP API to manage passwords, perform searches, etc. by using the SOAP API in any language that supports web services.

Who can use a Web API?

Web API can be consumed by any clients which support HTTP verbs such as GET, PUT, DELETE, POST. Since Web API services do not require configuration, they can be easily used by any client. In fact, even portable devices such as mobile devices can easily use Web API, which is undoubtedly the biggest advantage of this technology.

What is the major obstacle users faced when using SOAP?

When using SOAP, users often see the firewall security mechanism as the biggest obstacle. This block all the ports leaving few like HTTP port 80 and the HTTP port used by SOAP that bypasses the firewall. The technical complaint against SOAP is that it mixes the specification for message transport with the specification for message structure.

What are the common API testing types?

While there are certainly specialty tests, and no list can be asked to be comprehensive in this realm, most tests fit broadly into these following nine categories that you should remember before attending in an API testing interview. Validation Testing Functional Testing UI testing Load testing Runtime/ Error Detection Security testing Penetration testing Fuzz testing Interoperability and WS Compliance testing

What is the upper limit for a payload to pass in the POST method?

<GET> appends data to the service URL. But, its size shouldn't exceed the maximum URL length. However, <POST> doesn't have any such limit. So, theoretically, a user can pass unlimited data as the payload to POST method. But, if we consider a real use case, then sending POST with large payload will consume more bandwidth. It'll take more time and present performance challenges to your server. Hence, a user should take action accordingly.

Explain @RequestMapping annotation.

@RequestMapping annotation is used to map a URL to either an entire class or a particular handler method.

What is API Testing?

API testing is a kind of software testing which determines if the developed APIs meet expectations regarding the functionality, reliability, performance, and security of the application.

How often are the APIs changed and, more importantly, deprecated?

APIs, especially modern RESTful APIs, are a nice creation that can certainly simplify and accelerate integration efforts, which makes it more likely you will benefit from them. But APIs can and do change for various reasons, sometimes abruptly, and hence REST APIs do not differ from traditional integration methods in this respect. If an API call is obsolete and disappears, your procedure will interrupt and it is important to understand how often the APIs you depend on change or are deprecated.

What are main differences between API and Web Service?

All Web services are APIs but not all APIs are Web services. Web services might not contain all the specifications and cannot perform all the tasks that APIs would perform. A Web service uses only three styles of use: SOAP, REST and XML-RPC for communication whereas API may be exposed to in multiple ways. A Web service always needs a network to operate while APIs don't need a network for operation.

What are the core components of an HTTP request?

An HTTP request contains five key elements: An action showing HTTP methods like GET, PUT, POST, DELETE. Uniform Resource Identifier (URI), which is the identifier for the resource on the server. HTTP Version, which indicates HTTP version, for example-HTTP v1.1. Request Header, which carries metadata (as key-value pairs) for the HTTP Request message. Metadata could be a client (or browser) type, format supported by the client, format of a message body format, cache settings, and so on. Request Body, which indicates the message content or resource representation.

What is Annotation-based container configuration?

An alternative to XML setups is provided by annotation-based configuration which relies on the bytecode metadata for wiring up components instead of angle-bracket declarations. Instead of using XML to describe a bean wiring, the developer moves the configuration into the component class itself by using annotations on the relevant class, method, or field declaration.

What is an API?

An application programming interface (API) allows application developers to bypass traditional web pages and interact directly with the underlying service through function calls. It's s a software intermediary that enables two applications to communicate with each other. It comprises a number of subroutine definitions, logs, and tools for creating application software. In an API testing interview, you could be asked to give some API examples, here are the well-known ones: Google Maps API, Amazon Advertising API, Twitter API, YouTube API, etc.

What is AOP?

Aspect-oriented programming, or AOP, is a programming technique that allows programmers to modularize crosscutting concerns, or behavior that cuts across the typical divisions of responsibility, such as logging and transaction management. The core construct of AOP is the aspect, which encapsulates behaviors affecting multiple classes into reusable modules.