What Exactly Is An API?

According to Wikipedia,’An application programming interface (API) is an interface or communication protocol between different parts of a computer program intended to simplify the implementation and maintenance of software’.

API stands for Application Programming Interface. An API is a software intermediary that allows smooth communication between two applications.

APIs (Application Programming Interfaces), are the connecting layer between different layers of an application. Simply put, it acts as a messenger for applications, devices, and databases.

In addition, APIs are used for programming graphical user interface (GUI) components. A good API makes it easier for the developer to put all blocks together by providing all the building blocks.

The API layer contains the business logic of an application where the user’s interaction with services, data, and functions of the app is determined.

Since the API or service layer is in direct touch with both data and presentation layer it occupies a fixed space for continuous testing for QA and Developmental teams.

Applications have three layers:
Data layer
Service (API) layer
Presentation (UI) layer

What is API Testing?

Today, APIs are considered the epicentre of software development, connecting and transferring data and logics across disparate systems and applications. And testing them greatly improves the efficiency of the testing strategy as a whole, delivering faster software.

While traditional testing mainly focuses on the UI (User Interface), still it has many advantages to offer in API Testing. API Testing consists of making requests to single or sometimes multiple API endpoints and validate the response for performance, security, functional correctness or status check whereas UI Testing focuses on validating the look and feel of the web interface. Also, API Testing lays greater emphasis on business logic, data responses, and security and performance bottlenecks.

Various Types of API Testing

Unit Testing

Testing world is filled with misnomers, and simple and easy way for “unit test” and APIs is testing a single endpoint with a single request, looking for a single response.

Most of the time “Unit Test” is performed manually via command lines like “cURL” command or with lightweight tools like SoapUI.

Integration Testing

Integration testing is the most common form of API testing because APIs stay at the centre of integration.

End-to-End Testing

End-to-End testing can help us validate the flow of data and information between a few different API connections.

Performance Testing

Earlier load testing was difficult to execute in a CI/CD environment and was performed by a very few. LoadUI Pro is a performance testing tool for RESTful, SOAP, and other web services that enable nearly any team member to embed performance tests into their CI/CD pipeline.

Why API testing is required?

As the changes in software happen at a rapid pace, it becomes important to have tests that provide faster feedback for developers and testers. The major benefit of API testing is flexible access to the application without any user interface.

Testing the core, code-level functionality of the application provides an early evaluation of its overall build strength before running the GUI tests.

Various API Testing Tools

• JMeter
• Postman
• Rest assured
• Citrus Framework
• Fiddler
• Insomnia
• Powershell
• Taurus
• SoapUI
• Karate
• KatalonStudio
• TestNG
• Apiary
• Tricentis Tosca
• Swagger
• Apigee

For more details about API testing tool

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