API Testing

The five principles of API testing are:- 

1. Setup: The first principle of API testing is to create objects, initialize data and start services. Adopting this approach would ensure that there are no hurdles to API adoption caused by language. 
2. Execution: The second principle of API testing is execution, it applies steps to API and includes actions like logging. Adopting this principle aims to make the generated APIs as useful and problem-solving as possible. Implementers are more likely to devote time to practical solutions than theoretical or abstract ones. Interoperability is required if different enterprises share the same use case. 
3. Verification: The third principle of API testing is verification, it evaluates the result of execution. The goal of implementing this principle is to maximise the adoption of the specifications. The creation and publication of data on the server side, as well as its consumption and processing on the client side, must be considered when determining how simple a system should be.
4. Reporting: The fourth principle of API testing is reporting, it reports pass, fail, or blocked status. Adopting this principle makes it possible for the specifications to be executed in a range of languages and design paradigms. It is the outcome of combining the two earlier principles. 
5. Clean up: The fifth and last principle of API testing is clean up, it gives a pretest state. Adopting this principle will make sure that the requirements are cacheable while also being simple to comprehend and use. 

A common question in basic API Testing interview questions, don't miss this one.

There are many different types of API testing, which are: 

1. UI testing: Testing of the user interface for the API and other crucial components is referred to as UI testing. Instead of evaluating the API itself, UI testing concentrates primarily on the interface that connects to it. Although UI testing does not specifically examine API in terms of coding, it nevertheless offers a general assessment of the functionality, usability, and effectiveness of the front and back ends of the app. 
2. Functional testing: Functional testing includes testing certain codebase functions. These features serve as a depiction of particular circumstances to ensure that the API functions are used effectively and within the intended bounds. 
3. Security testing: By following this procedure, the API application is protected from outside dangers. Additional phases in security testing include verifying encryption techniques and the architecture of the API access control. User rights administration and authorization verification are also included. 
4.  Load testing: Load testing often takes place after a particular unit or the entire codebase has been finished. Using this method verifies that the theoretical solutions function as intended. The performance of the app is observed during load testing under both average and heavy loads. 
5. Penetration testing: The second trial in the audit procedure is penetration testing. Users who are unfamiliar with APIs will attempt to evaluate the threat vector from a distance, focusing on functions, resources, procedures, or the complete API and its constituent parts. 
6. Fuzz testing: Another phase in security auditing is fuzz testing. To find any forced failures or unfavorable behaviors, the system will be exposed to a large amount of random data, sometimes known as "noise" or "fuzz." This method puts the API's restrictions to the test to be ready for worst-case scenarios. 
7. Runtime testing and error detection: This sort of testing is concerned with how the API actually operates, in particular with the overall outcomes of applying the API codebase. This method focuses on one of the following: error detection, monitoring, execution errors, or resource leakage. 
8. Validation testing: The final stage of the development process is validation testing, which is crucial. It checks efficiency, behavior, and product features. To put it another way, validation testing can be thought of as a guarantee of proper development. 

There is a certain procedure followed for performing API, in addition to the standard SDLC process, API automation testing should at least include the following testing approaches: 

1. Testing for discovery: The test team should manually carry out the sequence of calls specified in the API, such as confirming that a particular resource accessible by the API may be listed, created, and deleted as necessary. 
2. Usability testing: This testing determines how user-friendly and functional the API is. And how effectively does API integration with other platforms 
3. Security testing: Testing for security includes determining the sort of authentication needed and whether or not sensitive data is encrypted over HTTP. 
4. Automated testing: The goal of API testing should be to produce a tool or a set of scripts that can be used to perform the API on a regular basis. 
5. Documentation: The test team must ensure that the documentation is sufficient and offers sufficient details to interact with the API. Including documentation in the final release is recommended. 

One must keep the following things in mind while performing API testing. Here are a few things to think about to make sure you get the most out of your tests throughout the product's life cycle if you want to get into API testing to gain the long-term rewards with less of a short-term burden. 

1. Verify and update the documentation already in place: You should initially spend some time looking for existing documentation and getting acquainted with how things are meant to work before starting any API testing for your project. You'll require information on the endpoints that are available, the request and return formats, the expected payload structures, etc. Building a trustworthy, maintainable test suite requires an understanding of how your APIs operate. 
2. Decide what you want to test first: The most frequent error any testing team may make when beginning their testing operations is to dive in headfirst without having a solid plan in place. Well before you make your initial API call, your efforts could be doomed if you don't know what needs testing first and, more significantly, what does not need any testing right now. Determining what to work on now and what to put off until later is crucial. Since you can't test anything, you must decide where to focus your efforts when you first start. 
3. Choose what to verify and keep an eye out for contradictions: There are numerous similarities between what has to be tested for APIs in most contemporary applications. You'll probably use XML or JSON to communicate with a REST or GraphQL API. Verifying various request types, the response body, the received status codes, any modifications in the resource's status, etc. are typical claims made for these settings. There isn't much variance in what you need to verify between various APIs unless such application has special requirements. 
4. Track down any potential security holes you may encounter: 

Whenever it comes to information, APIs may be powerful tools. An API endpoint can be created by a developer that returns a ton of useful data for use by another program. The developer may also give users control over the data that is returned. But just like with any software development, it's important to take extra precautions with APIs to make sure they're only creating the data that's required at the moment—neither more nor less. 

Testing the graphical user interface is known as UI (User Interface) testing. UI testing is focused on how the program looks and feels, including how the user interacts with its components like graphics, typeface, layout, etc. UI testing is different from API testing. API testing makes communication possible between two software systems. API satisfies the requirements for functionality, dependability, performance, and security. It does backend operations and is familiar with backend testing. Unlike UI testing, API testing focuses on the operation of the business intelligence. The business logic layer of the software architecture is the main focus. The appearance and functionality of an application will not be a focus of this testing.

A staple in API Testing interview questions and answers, be prepared to answer this one.

A bug is a mistake in software or hardware. While bugs are typically the product of programmer error or oversight, they can also enter a programme through compiler errors, false assumptions about how hardware or software interfaces work, or they can be purposefully incorporated into software to produce disguised interfaces or back doors. While vulnerabilities frequently result in software crashing or other unexpected effects, some bugs can be used to break into an otherwise protected computer system.There are many bugs we find in API testing, which are:- 

• Faulty error conditions
• Missing functionality
• Duplicate functionality
• Security
• Inconsistent error handling
• Performance
• Reliability
• Inconsistency
• Multi-threading issues 
• Flags

HTTP methods are an important concept for REST API testing interview questions. The following are the HTTP methods supported by REST API. 

• GET: This HTTP method is used to request a resource at the request URL. It usually gets discarded if it contains a request body. It is usually cached locally or on the server.
• POST: This HTTP method is used to submit information for processing and returns a new or modified resource. 
• PUT: This HTTP method is used for updating the resource at the request URL. 
• DELETE: This HTTP method is used to remove the resource at the request URL. 
• OPTIONS: This HTTP method tells us about the techniques that are supported. 
• HEAD: This HTTP method returns the meta-information about the request URL. 

Caching in REST API refers to storing copies of frequently accessed data to improve performance and reduce server load. 

Description: Caching is a technique used to temporarily store copies of data in a cache memory to speed up data access. In REST APIs, caching helps improve network efficiency by reducing the burden on servers. Frequently accessed data is stored in the cache, allowing subsequent requests to retrieve data quickly without querying the server again. 

Importance: 

• Performance: Reduces latency by serving cached responses quickly. 

• Efficiency: Decreases the load on the server and network. 

• Cost Savings: Reduces the need for repeated database queries, saving resources. 

Example: 

• GET Requests: By default, GET requests are cacheable. 

• POST Requests: Can be made cacheable if specified. 

Caching Example: When a client requests data using a GET request, the response is stored in the cache. If the same data is requested again, the cached response is returned, avoiding a full server round trip.

The act of damaging digital systems and networks by gaining unauthorized access to a computer system or account is a popular definition of hacking. Although hacking is not always harmful, it is most frequently linked to online crime and data loss by cybercriminals. 

Hacking is the term for using technology improperly to harm or destroy systems, obtain user data, steal data and documents, or obstruct data-related activity. Examples of such technology include desktops, cell phones, tablets, and networks. The stereotypical image of a hacker is a lone, miscreant programmer with advanced coding and system modification skills. However, this limited perspective does not account for hacking's underlying technological nature. 

Yes, it is possible. This is due to the fact that we are making requests via the internet, which mostly uses the HTTP protocol. This protocol is easy to read because it is text-based. Therefore, security testing of the APIs is necessary to create safer systems.  

After the initial level of testing each individual API, security testing typically begins. You make test cases with faulty requests in addition to legitimate inputs. All the so negative tests enable you to assess the effectiveness of your API error handling. Through the clever design of incorrect inputs that could crash your API or expose data, you can also utilize these negative tests to confirm the security of your API. Discovering API utilization and potential edge situations that are worth testing can be accomplished by gaining insight from tracing data using a variety of methods. APIs can be hacked easily while testing an API so we test the security of an API. When evaluating the API, we must validate two elements in order to check its security: 

• Authentication: Verifying that the end user's identification is accurate. 
• Authorization: Whether or not a person is authorized to access a resource. 

API tools are widely available and help developers accomplish their tasks more quickly. They contain solutions for programming, testing, debugging, writing documentation, and other related tasks. The use of API testing tools enables effective API testing and monitoring. Any kind of API is supported by it. The design of complicated tests for API verification, managing, and analyzing API testing, etc. is made possible by the API Testing tools solution. API Testing indeed is a difficult job, various tools are available for API testing a few of them are:- 

1. Postman 
2. SoapUI Pro 
3. Apigee 
4. Jmeter 
5. Karate DSL 
6. Airborne 
7. Swagger.io 
8. ReadyAPI 
9. ACCELQ 
10. Pyresttest 
11. REST-assured 
12. Katalon studio 

API is a powerful web component, and businesses of all kinds are embracing it because of the following advantages:- 

1.  Many businesses are understanding the value of API testing for delivering a positive customer experience. 
2.  API testing verifies that the built API satisfies the business's requirements.
3. Language-free: Any language can be used for test robotization because data is exchanged through XML and JSON positions. Since XML and JSON typically contain organized data, the check runs quickly and consistently. Additionally, similar information designs are used in libraries to assist in looking at the material. 
4. GUI-free: Prior to GUI testing, GUI-free programming interface testing can be conducted in the application. Early input and improved group profitability are implied by early testing. To find minor errors and evaluate the quality, try out the application's core capabilities. 
5.  Better test inclusion: The majority of API web administrations give information that enables you to create automated tests with high inclusion, including utilitarian testing and non-useful testing. 
6.  Rapid Release: Executing API testing typically takes eight hours compared to UI testing, allowing programming development teams to release products more quickly. 

1. Validation testing: One of the final and most crucial tasks in the development process is validation testing. It basically consists of a series of straightforward questions that are applied to the entire project, including product validation, API behavior on accessing the right data in the right defined manner, and the effective opportunity for any codebase to be removed or changed to get rid of deteriorations in the overall service. 
2. Security testing: By locating potential application flaws, security testing reveals vulnerabilities, threats, and hazards. The outcomes of security tests stop hostile attacks from outsiders as well as the loss of data, money, and reputation.
3. Runtime error testing: Critical flaws that become apparent during application execution are exposed through runtime error detection. An accurate detection report offers the chance to quickly pinpoint the underlying causes of application failure, unpredictable behavior, and inferior performance. 
4.  Performance testing: Applications that function poorly risk developing a negative reputation and falling short of business needs. Performance testing establishes measures for API scalability, stability, and performance under anticipated workloads. 
5. Functional testing: Functional testing employs the Black Box approach with no regard for the application's source code. The goal of functional testing is to ensure that the application is operating faultlessly. 

It's no surprise that this one pops up often in API Testing real time interview questions.

API documentation is like a deliverable. Technical content deliverables such as API documentation provide guidance on how to use and integrate APIs. It is a brief reference guide that includes all the details needed to use the API, including information on the functions, classes, return types, arguments, and more, all backed up with tutorials and examples. Traditionally, text editors and common content creation and maintenance tools have been used to create and maintain API documentation. Technical writing that describes the API is also known as API documentation. It contains guidelines for properly utilizing and integrating the API. The lifecycle of the API is also updated, including any new versions or retirements. Using Swagger or other documents, some portions of API documentation can be automatically generated.

The test cases that are run repeatedly during each sprint, such as regression cases, frequently need to be automated. Similar to this, there are several API testing scenarios that we must run before each release; these scenarios should be automated, and this is what we call API automation. We use various tools like SoapUI, apigee, etc., for API automation. The automatic creation of an API connecting two previously unconnected applications or services is the first application for API automation. If you can even find a competent API developer in the first place, manually developing an API can be a highly specialized and time-consuming project depending on the use case and technological complexity. With a project timetable of a few weeks or months, estimations for the cost of developing an API can rapidly reach the thousands and thousands of dollars range. Additionally, if the underpinning services change, these estimates do not take ongoing maintenance and support into consideration.

The first digit of the Status-Code element in a server response specifies the response class, and the last two digits play no part in classification. The Status-Code element are combination of 3 integers. A server responds to a request from a client by returning a status code. It includes codes from various specifications, IETF Request for Comments (RFCs), and some extra codes used in some widespread HTTP applications. One of five standard response classes is indicated by the status code's first digit. The normal message sentences that are displayed can be replaced with any human-readable alternative. The status code is a component of the HTTP/1.1 standard unless otherwise stated (RFC 7231).

Example: The error message "Page not found" will appear if the firm ABC changes its name to "ABD" and the user inputs the same old URL that has not yet been changed to the new company name. The code that pops up on the screen is the status code. Like error “404”.

There are a total of 63 status codes, but they are divided into 5 categories, and codes from each category are used for a different domain. The five categories are:- 

• 1xx informational response: This status code is used to provide information like a request was received or the action is in process. 
• 2xx successful: This status code is used to tell about the success or completion of an action or a process.
•  3xx redirection: This status code is used to give direction again, this status code is shown in cases where more steps need to be taken to complete the action.
• 4xx client error: This status code is shown when there is a client-side error. It usually pops up when there is a syntax error. 
• 5xx server error: This status code is shown when there is an error from the server side. It usually pops up when there is something wrong with the server, even though the request is valid. 

The capacity factor of a package or other data transmission unit is referred to as a payload in computing. The phrase, which has military roots, is frequently used in relation to malicious code that can be executed and cause harm. Data payload and malware payload are two different types of payloads that are used to attack and corrupt IT networks and systems, respectively. Data payload refers to the movement of data through a network.

Programmers use the term "payload" to distinguish between the information that is necessary for a piece of data and the information that is used to support it. Secured input data is supplied to the API as the payload/body in order to process the request. In the REST API, the payload is often built in JSON format.

API stands for application programming interface, it acts as a connecting link between a computer and its programs. It is a type of software interface that allows applications to access the data and interact with operating systems, software components and microservices. In simple terms, an API is responsible for sending the user's response to the system and bringing back the system's response to the user. APIs are used in web development both backend and frontend.

From this picture, we can understand how an API works. We can see how the API is accessing data from the database and making the communication between operating systems, computer programs and software components possible.  

API has been used in various technical projects by very prominent technological organizations. Some examples are Google Maps API, YouTube API, Amazon advertising API, etc. In the Google maps API project, navigation data from satellites was stored in the Google maps database and it was sent to the application with the help of an API. In the YouTube API, data from YouTube surveys and history was stored in the YouTube database and was then shared with the application with the help of API and was later used to curate YouTube videos and advertisements recommendations. Similarly in Amazon advertising API, data from customer history and orders were stored in the Amazon database and was provided to the software via API and was later used to curate tailor-made advertisements and product recommendations for each customer. In each project, the customer data collected by various surveys and research were stored in the database and were then provided to the software. The smooth communication that we witnessed in all the programs was due to the API.

No, it is not true that there are limited options for API testing. API testing methods are wide and varying. A few methods to test an API are: -

• Validation testing: Validation testing is a set of simple questions that are applied to the entire project. It is one of the last steps in the development process. It is done even after the verification of an API. The Validation testing includes some general questions about the product, behaviour, and efficiency.
  • Product: When we talk about products, we take into the count a few questions like was the correct product made? Was there an issue resolved within the limits of API building?, and did the API experience any code bloat or feature leak.
  • Behaviour: When we talk about behaviour we usually observe API and how is it dealing with the data, we ask questions like, Is API accessing the data in a proper defined method? Is the API accessing too much data? and is the data storage meets the confidentiality and integrity requirements of the dataset?
  • Efficiency: When we talk about Efficiency, we usually ask questions like, Is the API accurate, optimized, and efficient method of performing the required task? And do we need to add or alter any code base to enhance the efficiency and remove the impairments? 
• Functional testing: Functional testing is a test of specific functions within the codebase. The functions represent the specific scenarios that ensure that the API is functioning within the expected parameters. And even if the API is outside the expected parameters, function testing ensures that the errors are handled well. 
• UI testing: UI testing is the test of the user interface of the API and its constituent parts. It does not matter if the interface is graphical or it depends on command line endpoint calls, this test is only concerned with the functioning of UI.
• Load Testing: Load testing is done after the completion of a specific unit or the codebase as a whole, usually the test of the theoretical solution will work as a practical solution if the load varies. For example, if a software requests a certain data from an API, we have a solution for it, load testing will find what will happen if 1000 such requests were made.
• Runtime Error Detection: The runtime error detection test deals with the actual running of API. The other test is mostly concerned with the results of API, but this test is concerned with the universal results of utilizing the codebase of the API.
• Security Testing: Security testing is designed to ensure that when the API is implemented it is secure from external threats. It includes the Validation of encryption methodologies and validates access control.
• Penetration Testing: Penetration Testing is a step ahead of security Testing, in penetration testing the API is attacked by someone who has limited knowledge of the API. These attacks can be limited to functions, resources, processes or the constituent parts of the API.
• Fuzz Testing: In fuzz testing, massive amounts of random data often referred to as "fuzz" or "noise", are forcibly sent into the system to attempt forced crash, overflow, or negative behaviour. It prepares the API for the worst-case scenario.

Protocols indeed are an integral part of every digital system, Protocols are the set of rules that define how applications interact with each other. Protocols are a significant part of any API system since Protocols are responsible for interaction and communication. Protocols play a significant role in API testing as well. 

The various protocols used in API are: -

• HTTP 
• REST 
• SOAP 
• JMS 
• UDI 
• XML 

It is indeed true that API testing is a lengthy and rigorous process, there are many ways by which we test an API. We test an API because it is essential to do so and there are many advantages of testing an API. 

A few advantages of API testing are: - 

• Core functionality testing: It eliminates the need for a user interface, and provides access to the whole system. 
• Time and cost-effectiveness: API testing is less time consuming as compared to GUI (Graphical user interface) testing. Due to the time and cost-effective advantage that API provides it is widely used in web designing and development, to know more about it, click on the link below 

web designing and development course. 

• Language-independent: The data transfer that is done in API between the test platforms and computer applications is done using various protocols like XML and JSON and is completely independent of any language.
• Ease of integration with GUI: API testing is highly flexible and it helps in easier integration with GUI testing.

There are 5 significant principles involved in the API test design and they are as follows:-

• Setup: Setup involved basic initial steps like creating objects, starting services, initializing data, etc.
• Execution: Execution involves steps that we apply to API or the scenario which includes steps like logging.
• Verification: Verification involves the evaluation of the result of the execution.
• Reporting: Reporting involves the task of updating whether the execution has been passed, failed or blocked.
• Clean up: Clean up involves everything that comes under a pretest state.

Yes, there is a procedure that we need to follow when we are performing API testing. It involves some fundamental steps, which are:-

• Choosing the suite that we need to add to the API test case.
• Choosing the mode for test development
• Demanding the development of test cases that are required for the API methods.
• Configuring the control parameters of the application and then for the test conditions.
• Configuring the method validation
• Executing the API test
• Checking the test reports and filtering the API test cases
• Arranging all the API test cases

When we are performing API testing, there are a couple of things that we check. We check those things by raising a request to the API with the known data, and we analyze the validation response in this manner.

The basic things that we check during testing an API are: -

• Schema validation
• Status code of HTTP
• The accuracy of data
• Data type
• Data validation
• Data order
• Data completeness
• Response timeout implementation
• Authorization checks
• Error codes
• Security

API testing indeed has major advantages, but this does not mean it is bereft of any challenges. We face many challenges while API testing, few of them are: -

• Selection of parameter 
• Parameter combination 
• Call sequencing
• Providing input values
• Output validation
• Output verification

Various testing methods come under API testing, a few of them are: -

• Unit testing and Functional testing: It is used to test specific functions within the codebase
• Load testing: It is used to test the performance under load 
• Discovery testing: It is used to list, create and delete the number of calls that are documented in API 
• Usability and Reliability testing: It is used to get consistent results 
• Security and Penetration Testing: It is used to validate all types of authentication 
• Automation testing: It is used to create and run scripts that require regular API calls 
• End to end Integration and Web UI testing: It is used to test any software from start to finish. 
• API documentation testing: It is used to determine the efficiency and the effectiveness 

People often confuse APIs and web services because they can perform similar functions, but they are not the same. All web services are APIs, but not all APIs are web services. 

Description: APIs (Application Programming Interfaces) and web services are both used for communication between different software systems, but there are key differences: 

1. Network Requirement: 

• API: May or may not require a network to function. 
• Web Services: Always require a network to function.

2. Communication:

• API: Uses various communication methods including SOAP, REST, and XML-RPC. 

• Web Services: Primarily use SOAP, REST, and XML-RPC for communication. 

3. Usage: 

• API: Not all APIs are web services. APIs can be used for a wide range of functions. 

• Web Services: All web services are APIs designed specifically for network-based services. 

Example: 

• API Example: Amazon API used for accessing Amazon services. 

• Web Service Example: .NET SDK for network-based interactions. 

Comparison Table:

An API endpoint is a specific URL at which an API can be accessed by a client.

Description: API endpoints are the touchpoints where an API receives requests and sends responses. They define where resources are located on the server and how clients can interact with these resources. For example, in a RESTful API, an endpoint might be https://api.example.com/users to access user data.

Example: 

• Endpoint: https://api.example.com/users

• Function: Allows clients to interact with user resources, such as retrieving or updating user information.