What is API testing: comprehensive guide for testers and developers

Deeksha Agarwal

Posted On: April 26, 2018

view count40180 Views

Read time5 Min Read

API testing, a.k.a. Application Programming Interface testing, is the term which has garnered a growing attention in the past five years. It is a staple of any internet based product testing team, used for small stuff like image loading to huge stuff like payment processing.

Google trends on API testing

Google Trends showing popularity growth of API Testing for the past 5 years

API or application programming interface is a set of tools, protocols, program that glues all of our digital worlds altogether. If you are able to login to Medium, Quora, and other popular sites websites using ‘Login with google’, the main hero behind that is an API.

How API Made Our Lives Easier?

Remember the Trivago Guy?? Aggregator websites like Trivago bring you offer prices of various hotels from multiple sources like Expedia, Hotels.com, Goibibo etc, all in a single platform. A user can book a hotel and avail an offer rolled out by Expedia, without even logging into Expedia!!.

So, how this happens? The simple answer to your mind scratching question turns out to be API.

So, with the help of API your application can communicate with third party application without any human intervention, acting as a communication bridge in other words.

API Testing: What Led To The Growth?

Verifying that all the API endpoints act as expected without any breaks in between is the main aim behind API Testing. It is one of the most important aspects of a testing process because of:

1. Agile Practices

Organizations are lovingly embracing agile development therefore calling for the need of dramatically changed ways of automated testing. Continuous builds asks for continuous feedbacks and improvements and GUI tests tend to take longer to run in that case. Since API tests do not lean on UI to be done, hence match the frequency to keep in pace with Agile development.

download whitepaper

2. Internet of Things

IoT is no doubt gaining the pace and various sources predicts devices connected to IoT will keep growing and by the end of 2020 it will be 20 billion. Devices connected to cloud are highly backed by APIs. You won’t be launching satellites or developing google again to connect the devices in cloud, all we’ll be using will be API. So, it’s incumbent to make sure that the connected devices stay connected.

Where API Testing Stands in Services Based Architecture?

API testing service layers

Types of API Testing

Integration testing, security testing, performance testing, usability testing are some of the terms that you might be aware of as you’re here. Well, API testing provides shade to all the terms under a single umbrella. Let me put it that way, when you perform API testing you make sure that your API passes the following tests.

1. Functional Testing: To make sure that all the API endpoints are up and working and doing what exactly they are supposed to so.

2. Reliability Testing: Making sure that the API works in case of connecting it to various devices and don’t just get disconnected any time.

3. Load Testing: When various servers sends request to an API, it is necessary to make sure that the API responds to all of them.

4. Stress Testing: When more than set number of requests is received by the API how does it behaves? Does it send some message? Works as intended. Mandatory to check.

5. Security Testing: While giving authentication, it is important to make sure that no security breaches happen in between. No more than required data is shared. Have appropriate authentications, permissions, and access controls.

6. Integration Testing: All the APIs connected to each other communicate properly. And addition of features in the API do not cause addition of some bugs in other API modules.

7. Usability Testing: The API is functional and on the top of it, user-friendly.

Are you interested in learning more about API testing? Check out the TestuConf 2022 Phase Angle of API.

The Test Pyramid: Giving a Pump up to API Testing

Coupled with some major use cases like authentication, saving from the pain of writing the already written code, there are certain features that adds up to the need of API Testing.

One of them was well explained by Mike Cohn in his book Succeeding with Agile: Software Development Using Scrum with the help of test pyramid. According to which, automation test strategy calls for automating the different levels as:

Testing  Pyramid

Mike Cohn’s Testing Pyramid


The need for automating the tests increases from top to bottom. Unit tests forming the base of the pyramid calls to be automated first and the GUI tests forming the top are the ones required to be the least automated. But we are concerned about the ones spot in the middle: Service/API layer tests. Their proportion describes their relevance to be automated.

Furthermore, API automated testing takes far much less time than automated UI tests. In some cases, it just takes under 1 second to run a single end-to-end API test thus blending with the CI protocols.

So, the bottom line is that when you are developing an application, smooth communications with various other apps must be on top of your checklist. And API testing helps you complete that checklist.

Happy Testing!!!

Author Profile Author Profile Author Profile

Author’s Profile

Deeksha Agarwal

Deeksha Agarwal is in Product Growth at LambdaTest and is also a passionate tech blogger and product evangelist.

Blogs: 40