Interview Questions for API Testing: Expert Guide

Prepare for your API testing interview with our collection of questions for API.

Q.1. What is API?

ANS-1 APIs, or Application Programming Interfaces, facilitate seamless communication and data exchange between software systems. They serve as intermediaries, allowing applications to interact and perform functions through a standardized interface. With APIs, one software program can invoke specific functions or access data from another program.

Here’s how an API operates: When a request is received from a source, the API forwards it to a database, retrieves the requested data, and returns a response to the source. APIs abstract the underlying complexities, enabling users to interact with applications without needing to know the internal workings.

Notable examples of APIs include the Amazon API, which enables developers to integrate with Amazon’s e-commerce platform, and the Google Maps API, which provides access to mapping and location-based services.

Explore our curated collection of API testing interview questions to enhance your understanding of API testing methodologies, techniques, and best practices. Prepare yourself to confidently demonstrate your expertise in ensuring the functionality, security, and performance of APIs in your interviews.

Q.2. What is API testing?

Ans-2 API testing involves the direct testing of APIs, serving as a critical component of integration testing to verify that APIs meet desired expectations in terms of application functionality, reliability, performance, and security. By conducting API tests on multiple API systems, testers can thoroughly assess the behavior and interactions of APIs.

This form of testing primarily concentrates on the business logic layer within the software architecture. By examining the API endpoints, input parameters, and expected outputs, testers can evaluate how well the APIs adhere to the intended functionality and business rules.

API testing serves as a valuable approach for ensuring the seamless integration and proper functioning of APIs within the overall software ecosystem. By validating the API behavior and responses, testers can identify any anomalies or deviations that may impact the overall system performance or user experience.

Q.3. What types of API tests are there?

Ans-3 API testing includes the following types of tests:

Unit Testing:-Developers perform unit testing to ensure that each component of the software system functions correctly and meets its intended purpose.

Function Testing:-Testers conduct functional testing to verify whether the software system functions correctly based on the specified requirements.

Load Testing:-Load testing evaluates the performance of a software system under expected and peak load conditions.

Runtime/Error Detection:-During runtime/error detection testing, testers monitor the system’s behavior in real-time to capture unexpected events, crashes, or error conditions.

Security Testing:-Testers perform security testing to identify vulnerabilities and weaknesses in the software system’s security mechanisms.

UI Testing:-UI testing focuses on validating the user interface of a software system. Testers evaluate the visual aspects, interaction, and responsiveness of the user interface, ensuring that it functions correctly and provides a seamless user experience.

Interoperability and WS compliance Testing:-

Interoperability and WS compliance Testing:-WS compliance testing specifically focuses on verifying the compliance of web services with industry standards and protocols.

Penetration Testing:-Ethical hackers perform penetration testing to assess the vulnerabilities of a software system. They simulate real-world attacks, attempting to exploit security weaknesses and identify potential threats and risks.

Fuzz Testing:-Testers conduct fuzz testing by feeding unexpected, invalid, or random inputs to a software system to assess its robustness and resilience against unforeseen data. They aim to identify potential crashes, memory leaks, security vulnerabilities, or other unexpected behavior caused by malformed or unexpected inputs.

Q.4. What protocol is used in API testing?

Ans-4 The protocols used in API testing are:

HTTP:-(Hypertext Transfer Protocol): HTTP is the primary protocol used in web-based APIs. It enables communication between clients (such as browsers or applications) and servers. API testing often involves sending HTTP requests (such as GET, POST, PUT, DELETE) to the API endpoints and analyzing the HTTP responses.
REST:-(Representational State Transfer): REST is an architectural style for designing networked applications. RESTful APIs use HTTP as the underlying protocol and follow specific principles for resource-oriented communication. API testing of RESTful APIs involves sending HTTP requests to different endpoints, handling HTTP status codes, and validating responses in JSON or XML formats.
SOAP:-(Simple Object Access Protocol): SOAP is a protocol for exchanging structured information in web services. It uses XML for message formatting and operates over various transport protocols, including HTTP, SMTP, and others. API testing of SOAP-based APIs involves sending SOAP requests, handling SOAP envelopes, and validating the XML-based responses.
JMS:-(Java Message Service):is a Java-based messaging standard that enables applications to exchange messages asynchronously. It provides a reliable and flexible means of communication between distributed systems, allowing components to send, receive, and process messages in a decoupled and asynchronous manner.
UDDI:-(Universal Description, Discovery, and Integration): is a directory service standard that facilitates the discovery and integration of web services within a networked environment. It enables businesses and organizations to publish, discover, and consume web services, making it easier to locate and interact with services provided by different entities.

Q.5. What tools are used for API testing?

ANS-5 When it comes to API testing, selecting the right tool is crucial to ensure the quality, reliability, and performance of your APIs. In this article, we will delve into a comparison between two popular API testing tools: Parasoft SOAtest and Postman.

Parasoft SOAtest: Parasoft SOAtest stands out as a comprehensive API testing tool that simplifies and streamlines the testing process. It offers a wide range of features that encompass both functional and non-functional testing aspects. Testers can effortlessly validate API behavior, conduct regression testing, and evaluate performance, security, and compliance factors.

Let’s explore some key features of Parasoft SOAtest:

End-to-End Testing: Parasoft SOAtest enables testers to perform end-to-end testing by simulating various components of a distributed application architecture.It supports testing APIs across different protocols, including REST, SOAP, JMS, AMQP, and more.

Test Creation and Execution: With an intuitive graphical interface, Parasoft SOAtest empowers testers to create complex test scenarios easily. Test cases can be built using drag-and-drop actions, ensuring accessibility for testers with varying technical expertise. The tool also offers the flexibility to automate tests, delivering repeatable and consistent results.

Service Virtualization: Parasoft SOAtest includes robust service virtualization capabilities, enabling testers to simulate dependencies and create virtual services for API testing. This feature proves invaluable when testing APIs with external dependencies or APIs that are still under development.

Security and Compliance Testing: Parasoft SOAtest incorporates built-in security testing capabilities, aiding in the identification of vulnerabilities, such as potential security threats, unauthorized access, and data breaches. The tool also provides compliance testing features to ensure APIs adhere to industry standards and regulatory requirements.

Postman: Postman, a widely adopted API testing tool, is renowned for its simplicity, user-friendly interface, and extensive collaboration features. It primarily focuses on functional testing and API documentation.

Let’s delve into some key features of Postman:

1. Request Creation and Testing: Postman offers a user-friendly interface that facilitates the creation and sending of API requests. Testers can easily customize requests, set headers, and handle authentication methods like Basic, Digest, OAuth, and more. Additionally, Postman allows the creation of test scripts using JavaScript, enabling the execution of complex test scenarios.
2. Collections and Environments: Organizing requests into collections is seamless with Postman, enabling testers to manage and execute sets of related tests efficiently. Environments can be created to manage variables and configurations, facilitating testing across different environments or test data sets.
3. Collaboration and Documentation: Postman excels in collaboration features, enabling teams to share and collaborate on API testing. The tool offers options to share collections, run tests in the cloud, and generate API documentation with detailed descriptions and usage examples.
4. Integration and Automation: Postman seamlessly integrates with other development tools and platforms, including CI/CD pipelines and test management systems. It provides features such as command-line interface (CLI) support, test automation, and integration with popular version control systems.

In conclusion, both Parasoft SOAtest and Postman are powerful tools that can effectively support your API testing efforts. Assess your project needs, evaluate the features and capabilities of each tool, and choose the one that aligns with your testing objectives and team requirements. Regardless of the tool you choose, performing thorough and systematic API testing is vital for delivering high-quality APIs that meet user expectations and ensure a seamless integration experience.

Q.6. What is an API Framework?

Ans-6 A framework or software framework is a platform for developing software applications. An API framework is the foundation upon which software developers can build applications for a specific platform.
For example: Frameworks can contain predefined classes and functions that can be used to process input, manage hardware devices, and interact with system software.
A framework is similar to an application programming interface, and technically a framework contains an API. Frameworks serve as the basis for programming, and APIs provide access to elements supported by frameworks. Frameworks also include code libraries, compilers, and other programs used in the software development process.

An API framework is defined by a configuration file that contains a list of all APIs that must be enabled and enabled for a particular program execution.

Q.7. Can resources be created using GET requests?

Ans-7 The PUT or POST method is used to create resources. GET is only used to request resources.

Q.8. What are the components of an HTTP request?

Ans-8 An HTTP request consists of 5 components as:

• Action : An action indicates an HTTP method such as GET, PUT, POST, DELETE.
• Uniform Resource Identifier (URI): A URI is an identifier for a resource on a server.
• HTTP Version: Specify the HTTP version, such as HTTP V1.1.
• Request Headers: Request headers contain metadata for HTTP request messages. Metadata includes client type, client supported formats, message body format, cache settings, and more.
• Request Body: The resource body specifies the message content or resource representation.

Q.9.What is API documentation?

Ans-9 Good documentation is a must for any foundation. The API documentation serves as a quick reference for accessing the library and working programmatically. If such documents are used, they should consist of good planning, content sources, good layout, information about each feature, etc. There are various documentation tools such as Doxygen and JavaDoc.

Q.10.What types of errors can be detected during API testing?

Ans-10 API tests help find many kinds of bugs.

Stress
Security
Duplicate or missing functionality
Reliability
Unused flags
Performance
Incompatible error handling
Multi-threaded issue
Improper errors

Q.11. What are URIs? What is the purpose of a web-based service ?

Ans-11 URI stands for Uniform Resource Identifier. This is a string designed touniquelyidentify resources and extensibility by URI scheme. The purpose of the URI is to locate the resource on the server hosting the web service.

Q.12. Which HTTP protocols does REST support?

Ans-12 GET: GET is used to request data from a specific resource.GET requests can be cached and bookmarked. It remains in your browsing history and has a length limit. Do not use GET requests when working with sensitive data.

POST: POST is used to send data to the server to create or update resources.POST requests are never cached or bookmarked.
PUT: PUT replaces the current representation of the target resource with the request payload.
DELETE: DELETE deletes the specified resource.
OPTIONS: OPTION is used to describe communication options for the target resource. HEAD: HEAD requests a response. This is the same as a GET request, but without the response body.

Q.13. What are the challenges in API testing?

Ans-13 The challenges during API testing are:

• Parameter selection
• Combination of parameters
• call sequence
• Verification and verification of output
• The main challenge is to provide input values, which is very difficult as there is no GUI available.

Q.14.What is a resource in REST and how can a resource be represented in REST?

Ans-14 The REST architecture treats any content as a resource, including text files, HTML pages, images, videos, and dynamic business information. A REST server provides the ability to access and modify resources. Each resource can be identified by a URI/Global ID. REST uses different representations to define resources such as text, JSON, and XML. The most common representations of resources are JSON and XML.

Q.15. What exactly should an API test check?

Ans-15 During an API test, testers actively utilize known data to send a request to an API and analyze the response. The primary objective is to actively verify the accuracy of the data and assess various parameters and aspects of the API’s behavior.

Key elements evaluated during an API test include:

1. HTTP Status Code: Testers actively examine the returned HTTP status code to determine if the request was successfully processed or if any errors occurred.
2. Response Time: Actively measuring the response time helps assess the API’s performance and ensure it meets the defined requirements.
3. Error Code Handling: Testers actively check for error codes in the API response to identify and handle any errors that might have occurred during the request processing.
4. Data Accuracy: Active verification is performed to ensure the accuracy and integrity of the data returned by the API, comparing it against the expected results.
5. Eligibility Confirmation: In certain scenarios, testers actively confirm eligibility criteria to ensure that the API functions correctly based on specific conditions or requirements.

Additionally, API testing extends beyond functional testing. Testers actively conduct non-functional tests such as performance tests to evaluate the API’s responsiveness and scalability, as well as security tests to assess its vulnerability to potential threats.

By actively conducting API tests with known data and thoroughly analyzing the responses, testers can ensure the accuracy, reliability, and performance of the API, along with meeting various non-functional requirements.

Q.16. What are the typical tests performed on the API?

ANS-16 Common tests performed on the API are:

• Additionally, it is crucial to actively validate API responses based on the corresponding requests. Testers should actively ensure that the returned values align with the expected outcomes defined in the request.
• During API testing, it is important to actively verify that the system accurately validates the results when an API updates a data structure. This involves actively checking that the changes made through the API are correctly reflected and processed by the system.
• Another aspect to consider is actively checking whether the API raises additional events or triggers other API requests during its execution. This helps ensure that the API functions as expected in terms of actively triggering the necessary actions or workflows within the system.
• Furthermore, it is essential to actively examine the behavior of the API when no value is returned. Testers should actively verify that the API handles such scenarios appropriately, whether by returning a predefined response or actively signaling the absence of data in a clear and expected manner.
• In API testing, testers should actively pay meticulous attention to validating and assessing the API responses to ensure they actively align with the corresponding requests, actively update data structures, actively trigger the necessary events or API calls, and actively handle scenarios where no value is returned. This proactive and comprehensive approach actively helps maintain the integrity and reliability of the API interactions within the overall software ecosystem.

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