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As you all know, API stands for Application Programming Interface, which is a software intermediary that allows two applications to talk to each other.

For example, you are booking a flight through online travel site. You will fill out the necessary information like departure and arrival city, date of travel, passenger details and so on. And you click “Search”. API comes into action here; When you click the search button and then the site interacts with each airlines API, which delivers results that meets your criteria. And all this happens in seconds because of an API, which acts like a messenger that runs back and forth between applications, databases, and devices.

What is API Testing?

API testing is a type of software testing where application programming interfaces (APIs) are tested to determine if they meet expectations for functionality, reliability, performance, and security.

In API testing, our main focus will be on a Business logic layer of the software architecture. API testing can be performed on any software system which contains multiple APIs. API testing won’t concentrate on the look and feel of the application. API testing is entirely different from GUI Testing.

Why API Testing?

If an API doesn’t perform efficiently and effectively, it will never be included in a software system. An error at the API level can break the flow of the entire application as a chain of integrated business processes will be disrupted. Here are some common reasons why you should test your APIs:

  1. It is to ensure the API does what it’s supposed to do.

  2. It is to ensure that the API can handle the load.

  3. It will help to detect the ways the users can mess things up.

  4. To ensure that the APIs work across devices, browsers, and operating systems.

  5. With API testing there could be costs involved due to system failure.

Benefits of API Testing: Language-independent: Data is exchanged via XML and JSON formats, so any language can be used for test automation. XML and JSON are typically structured data, making the verification fast and stable. There are also built-in libraries to support comparing data using these data formats. GUI-independent: API testing can be performed in the app prior to GUI testing. Early testing means early feedback and better team productivity. The app's core functionalities can be tested to expose small errors and to evaluate the build's strengths. Improved test coverage: Most API/web services have specifications, allowing you to create automated tests with high coverage — including functional testing and non-functional testing. Faster releases: It is common that executing API testing saves up to eight hours compared to UI testing, allowing software development teams to release products faster.

Types of API Testing:

API testing typically involves the following practices:

  • Functionality Testing – To check if the API works and does exactly what it’s supposed to do.Includes testing particular functions in the codebase. These features are the representation of specific scenarios to make sure the API functions are handled well within the planned parameters.

  • Reliability Testing – To check if API can be consistently connected to and lead to consistent results.

  • Validation Testing – Helps verify the aspects of product, behavior, and efficiency of an API.Validation testing occurs among the final steps and plays an essential role in the development process. In other words, validation testing can be seen as an assurance of the correct development.

  • Runtime and error detection This testing type is related to the actual running of the API - particularly with the universal results of utilizing the API codebase. This technique focuses on one of the below aspects: monitoring, execution errors, resource leaks, or error detection.

  • Load Testing – Is performed to ensure the performance of API under both normal and at peak conditions.Load testing generally occurs after a specific unit or the whole codebase has been completed. This technique checks if the theoretical solutions work as planned.

  • UI Testing – It involves testing the user interface for the API and other integral parts. UI testing focuses more on the interface which ties into the API rather than the API testing itself. Although UI testing is not a specific test of API in terms of codebase, this technique still provides an overview of the health, usability, and efficiency of the app’s front and back ends.

  • Security Testing – To test that the API is secure against all possible external threats.Security testing also includes additional steps such as validation of encryption methodologies, and of the design of the API access control. It also includes user rights management and authorization validation.

  • Penetration Testing – To detect vulnerabilities of an application from an attackers perspective.Penetration testing is considered the second test in the auditing process. In this type, users with limited API knowledge will try to assess the threat vector from an outside perspective, which is about functions, resources, processes, or aim to the entire API and its components.

  • Fuzz Testing – To test the API in terms of the limits to prepare for the “worst case scenarios”.Fuzz testing is another step in the security audit process. In fuzz testing, a vast amount of random data (referred to as "noise" or "fuzz") will be input into the system to detect any forced crashes or negative behaviors.

Various API Testing Tools(

Basically, what exactly needs to be verified in API testing is when we send a request to the API with the known data and we analyze the response. We check for

  • Data accuracy

  • HTTP status codes

  • Response time

  • Error codes in case API return any errors

  • Authorization checks

  • Non-functional testing such as performance testing, security testing.

Application Programming Interface (API) is the brain that connects the world. It is the set of tools, protocols, standards and code that glues the digital world together. A good API is the secret to testing earlier that is helpful in finding problems earlier in the Software Development Life Cycle (SDLC), which further prevents delays, saves time, ensures the efficiency of the conducted tests and makes the process of testing easier. It is API that provides value to the application and ensure that it performs and functions perfectly.

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