Current Date :June 15, 2024

Introduction to API testing and best tools for it

What is API?

Application Programming Interface, popularly known as API, is an intermediary software that allows two applications or systems to communicate in the required manner. To help you get a better understanding, let us take you through an example. Imagine you are searching for travel packages for your trip to Bali on a website. Once you type in the details like the travel dates, type of hotels you want to stay and so on, the website gets in contact with the APIs of different travel websites to identify the ones that match your requirements. What happens during the seconds in between you putting your requirements and getting the results is done by an API.

Now that you have a clear understanding of what an API is, you must now have an idea of how important it is to test this function in a system. If the API does not work the way it is intended to and in a secure manner, it is almost impossible to run the software efficiently. This is where API Testing comes into play, as it inspects whether the intermediary software works the way it should.  

What is API Testing?

To put it in simple words, API Testing is a type of software testing phase that takes place to check if the API works in the desired manner in terms of functionality, performance, reliability and security. The aim of the API Testing is to reveal the bugs and errors in the expected behaviour of the API.

An application, in general, has three layers – Presentation Layer or UI, Business Layer or AUI and Database Layer. The API Testing is conducted on the business layer to check if the processing of the logics and codes is carried out the right way or not.

Why should we perform API Testing?

API Testing surely improves the functionality of the business layer but it has other benefits as well when compared to the commonly used GUI Testing.

  • Perform tests irrespective of the language and GUI – One of the biggest advantages of API testing is that the language of the program does not matter. Since all the data is exchanged via XML and JSON, one can use any language to create the tests, irrespective of language used to develop the application at first place. Similarly, there is no need for a user interface to check for the errors in the core functionality of the API.
  • Can automate most tests – A really big reason why testers around the world are switching to API Testing is because of the fact that most of the tests involved in it can be automated. As a result, you can improve the test coverage by a considerable margin.
  • Reduces the costs – Since API Testing is done at a much earlier stage, you can find the errors and bugs much earlier than usual and fix them early on. Since you are not allowing the bugs to create a huge problem later on in the program (as is the case in GUI Testing), you can save a lot of money.
  • Get faster releases – During a typical UI regression testing phase, tests take up 8-10 hours during its execution but they only take 1-2 hours during API Testing. This directly translates to companies being now capable to churn out faster releases.

How should you perform API Testing?

  1. Document all API Testing requirements – The first step is to plan everything you need to do throughout the testing phase. The purpose, the workflow, the integrations you want, the features you want to test – everything should be jotted down so that you clearly know what is to be done.
  2. Set up the test environment – With the required set of parameters involved in the API, you need to set up the test environment. This step also involves the configuration of database and server for the overall application requirements.
  3. Integrate application data – The next step involves integrating all the application data to the test cases and running them against all the user-input possibilities.
  4. Decide the type of tests you want to conduct – There are several types of testing that are involved in an API Testing phase, like functionality testing, load testing, security testing, fuzz testing and many more. Once the test boundaries and requirements are created, it is important to make sure that the right types of tests are being used.
  5. Execute and Report the tests – Now that the tests to be performed are known, the last step is to create the test cases around them and execute the tests. Documenting and reporting the test results is important, as it helps you in creating further tests and also while repeating the test cycles.

API Testing tools

Postman – It is one of the most popular API testing tools in the industry with more than 4 million users. The best part about this tool is that is compatible with Mac, Windows, Chrome and Linux apps, making it possible for you to test most APIs out there. It documents and monitors the test features simultaneously while running the tests.

Paw – It is probably the best API testing tool for Mac-native HTTP APIs. It not only lets you build HTTP requests and check the server’s response but generate codes as well. You can sort by host and name, make group and organize requests and has a bunch of various other user-friendly features.

SoapUI – This is a testing tool that is wholly dedicated to API testing and hence can accommodate even the most complicated test scenarios. You can perform asynchronous testing as well with this tool. You can use Groovy to create custom codes in this tool when required. Furthermore, creating a test with this tool is easy, as it has a simple drag and drop function.

JMeter – It is an open-source tool that was made to initially perform load testing but with its integration with Jenkins, it now supports a myriad of API functionalities. It can be used in both static and dynamic resource performance testing. Furthermore, it allows testers to replay the tests when required.

Katalon Studio – If you are looking for a common platform to create and execute API/web services, mobile testing and UPI functions, then the Katalon Studio is the tool to use. It has one of the best assertion libraries, thus helping you get a robust performance. Also, it supports a data-driven approach to perform the tests, making it quite reliable.

If you are looking for efficient testers to perform API testing for your software, then get in touch with TestUnity. We use the best API testing tools in the industry to give you reliable results with a quick turnaround time so that you can release your product in the market on time.


Testunity is a SaaS-based technology platform driven by a vast community of testers & QAs spread around the world, powered by technology & testing experts to create the dedicated testing hub. Which is capable of providing almost all kind of testing services for almost all the platforms exists in software word.

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