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What Is API Testing?

APIs have quickly become the epitome of software development. Testing your APIs improves the efficiency and speed of your testing strategy and helps you deliver the software even better. But what is API testing? Let’s explore this process a little further.

Application programming interfaces

Applications usually have three layers: a service layer (API), a data layer, and a final presentation (UI) layer. Application programming interfaces (APIs) are used in connecting multiple layers or different systems. The service layer contains the logic of an application. Business logic in applications is basically ruling on how the users interact with functions, data, and services of the developed app. 

For many QA and development teams, the API layer presents a good spot for continuous testing since it’s in contact with both the UI and the data layers. In conventional testing, developers mostly focused on testing the presentation layer. But currently, testing the APIs is becoming more of a focus.

Testing the APIs

Although there are many approaches to testing APIs, the testing process essentially consists of several requests to multiple or a single API endpoint and the validation of the response generated. API testing can be done for several reasons, such as status checks, security, performance, or functional correctness. 

Primarily, API testing puts more emphasis on testing logic, security, performance bottlenecks, and data responses. It also focuses on testing the look and feel of a web interface and the functionality of a payment button.

Automated testing vs. manual testing

There are several ideal situations for using either manual or automated API testing. Manual testing is cumbersome since it involves writing your testing code, while automated testing involves the use of a testing tool. 

In the world of agile developments, DevOps and continuous delivery, automated testing is highly recommendable. Some of the scenarios that call for automated testing include:

  • Dynamic testing
  • Functionality testing
  • Functional test coverage analysis
  • Protocol testing in unified frameworks
  • Testing for errors
  • Tests being carried out in multiple languages.

Manual testing comes in handy in scenarios such as ad-hoc testing, usability, and exploratory testing.

How testing is done

Requests must be sent through another application since APIs typically lack an interface. Therefore, methods like black-box testing are not possible in testing APIs. Instead of sending requests to the endpoints and recording the response for analysis, the application can be used to test APIs either as part of an integrated system or directly. Here are a few key considerations made in API testing.

Configuring the API testing environment

You might need to set up the server and database depending on the infrastructure of the app that’s being tested. Luckily, most scenarios only require that you know how and where to address the application’s components and then install the testing tools.

API test tools

The recent rise in popularity with API testing has caused a spike in the number of API test tools. There are several open-source API testing tools, as well as commercial test tools. The commercial tools are available in paid professional versions or free lower-level versions with limited functionalities.

Test protocols

Most developers use protocols (such as SOAP and REST) to develop their APIs. When testing, you should pay close attention to the use of custom protocol implementation that may have special parameter settings and handling requirements.

Performance of the APIs

Tools like Jmeter are helpful because API tests can quickly be converted to a performance test. Other commercial and open-source tools can be used, too, depending on the client’s application.

Different parameters

Some rules may require different parameters and sequencing. This is very common in cases where the business rules have different API implementations. This is also why testers must be well-versed with product business rules that have special implementation requirements.

Advantages of API testing

Compared to GUI testing, API testing is more time effective. With the API tools, testing for APIs requires less code and provides broader test coverage.

API tests save you money since they can be used to identify minor bugs before they become bigger. It’s cost-effective for any application developer to identify and fix minor bugs in the initial stages.

Another benefit is that tests can be carried out in multiple languages. The automated API testing can handle multiple testing languages.

Testing for core functionality is important for any software development. With API testing, APIs can be tested even without an interface. For other tests, like GUI testing, the application has to be complete to test core functionalities.


API testing is highly required and quite crucial. Learn how you can incorporate API testing into the development of your new software to improve functionality and reduce the risks.



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