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API Testing: What is it and why is it important?

What is API Testing?: How to Do It, Automation Tools & More

Imagine you’re at a restaurant, and no one was there to take your order. Instead, you look at the options on the menu and go to the chef in the kitchen to make your request. If the option you wanted was not available, you may have to go back to your table to look at the menu again and decide on something else. That would be a tiresome experience.  

The whole process might be a lot easier if the restaurant had a waiter who could go between the diner and the chef. In software, an API (Application Programming Interface) is used to communicate between two software systems. Just as a waiter can modify your food to your liking, give your requests to the chef, and bring your food back, an API takes requests and fetches the response from the server, and different parameters can be added to the requests. 

An API serves as an engine for a software application, playing a crucial role for it to function without any errors. A perfectly functioning API is the key to a seamlessly running application. Nevertheless, it is essential to test the API as it proactively prevents and resolves potential issues that might emerge in the application’s later stages.

What is API testing?

API testing is a type of software testing performed to verify that API fulfills its expected functionality. By conducting testing on a collection of APIs, we can verify they work without deviations and errors. Furthermore, API testing reduces the probability of detecting defects at a later stage, indirectly reducing the cost of testing. 

API testing not only aids in identifying and addressing security vulnerabilities but also allows testers to explore various parameters and simulate potential phishing attacks. Additionally, API testing can be used to do a performance check, as it serves as the bridge for data retrieval.  

How is API testing done?  

API testing is typically performed by QA testers using the following approaches: 

  • Connecting to the API endpoint and making calls to it directly.
  • Executing the requests against multiple endpoints simultaneously.
  • Testing different versions of the endpoints using environmental variables. 

To test an API, the QA team should consider the following:  

  • What testing endpoints are available? 
  • What type of response codes should successful queries have? 
  • What kind of error messages are to show up in a declined request?   
  • Developing the API test suite based on the business level understanding.

What kind of bugs can be found in API testing? 

There are several types of bugs that can be identified through API testing. 

  • Error handling failures – API endpoints need to have error handling in place to show the right message if it receives invalid data. While testing, we verify that there are no error handling failures and exceptions. 
  • Missing /duplicate functionality – If an API misses an endpoint, that means the requirement has not been fulfilled by that API. At the same time, if there is a duplication of API implementation, it leads to confusion and compatibility issues. So, in API testing, we verify to make sure there is no duplication or missing functionalities. 
  • Reliability – API is verified for reliability issues like downtime to make sure the user doesn’t have a poor experience.  
  • Security – In API testing, we make sure only authorized users are able to access the APIS to prevent data breaches. 
  • Performance – API response time needs to be verified under a load while doing API testing to avoid poor user experiences.

API Testing Automation 

Automation of API testing adds significant value to the quality of an application. There are a wide range of tools available for testing APIs. Postman is one such API client that can be used to develop, test, and document the APIs. The advantage of using Postman is that you don’t have to build the framework to test the endpoints. It helps in hitting the API endpoints by quickly creating the requests as per the API specifications. This streamlined approach saves time and effort, ultimately contributing to the overall efficiency and effectiveness of API testing.

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