Every user in this world expects the software to do wonders and interact with the other application to give uninterrupted service. To meet such requirement companies of all sizes are moving towards API-driven software architecture.

Any company can create an application that sends an impulse to a public API and receives a certain response. This enables coherent communication and information exchange between multiple software systems from multiple software companies.

What is API Testing?

API (Application Programming Interface) enables communication and data exchange between two separate software systems. It also involves testing application programming interfaces directly and as part of integration testing to determine if they meet expectations for functionality, reliability, performance, and security.

Ola and Uber’s applications are real-world examples of how APIs are used by developers to integrate functionality developed by other companies. When you book a cab using ola or uber the application doesn’t know how to find the route so it will call the google map API and wait for it to fetch. The entire process will look so easy and completed within a second, it also seems as if everything were happening right in the app. 

What are the types of API Testing?

API testing typically involves the following practices:

  • Functionality Testing – To check if the API works and does exactly what it’s supposed to do
  • Reliability Testing – To check if API can be consistently connected to and lead to consistent results
  • Validation Testing – Helps verify the aspects of product, behavior, and efficiency of an API
  • Load Testing – Is performed to ensure the performance of API under both normal and at peak conditions
  • UI Testing – It involves testing the user interface for the API and other integral parts
  • Security Testing – To test that the API is secure against all possible external threats
  • Penetration Testing – To detect vulnerabilities of an application from an attackers perspective
  • Fuzz Testing – To test the API in terms of the limits to prepare for the “worst case scenarios”

Challenges of API Testing

  • There is no GUI, which will make it difficult for testers to give input values
  • Test case management is difficult since a tester might have to deal with millions of test cases
  • The tester must possess expertise in the programming language(s) that are targeted by the API
  • Time-consuming, requires a lot of time and resources to develop tools and design tests
  • Improper documentation will make it difficult for a test designer to understand the purpose of API calls
  • Proper call sequencing is required as this may lead to inadequate coverage in testing
  • Exception handling functions need to be tested thoroughly

Most Popular API Testing Tools in the Market

Katalon Studio

API Testing Tools-Katalon Studio

Katalon Studio is an automation testing solution developed by Katalon LLC and the first public release was made in September 2016. The main programming language used in Katalon Studio is Groovy and Java. Katalon Studio is available for Windows, macOS, and Linux. Find the other similar Katalon products below,

Katalon Recorder is a browser add-on for recording user actions in web applications and generating test scripts, called Katalon Recorder.

Katalium is a framework that provides a blueprint for test automation projects based on Selenium and TestNG.

Katalon TestOps is a web-based application that provides visualized test data and execution results through charts, graphs, and reports.


API Testing Tools-SoapUI

SoapUI is an open-source web service testing application for Service-Oriented Architectures (SOA) and Representational State Transfers (REST). SoapUI was initially released to SourceForge in September 2005. 

Since the initial release, SoapUI has been downloaded more than 2,000,000 times. It is built entirely on the Java platform and uses Swing for the user interface. This means that SoapUI is cross-platform.

Today, SoapUI also supports IDEA, Eclipse, and NetBeans. SoapUI can test SOAP and REST web services, JMS, AMF, as well as make any HTTP(S) and JDBC calls

SoapUI provides extensive options for scripting, using either Groovy or JavaScript, making it possible to create complex testing scenarios and add custom functionality.


API Testing Tools-Postman

Postman is currently one of the most popular tools used in API testing. It started in 2012 as a side project by Abhinav Asthana to simplify API workflow in testing and development. It offers a sleek user interface with which to make HTML requests, without the hassle of writing a bunch of code just to test an API’s functionality.

Postman is a powerful tool for performing integration testing with your API. It allows for repeatable, reliable tests that can be automated and used in a variety of environments and includes useful tools for persisting data and simulating how a user might actually be interacting with the system.

You can attach test scripts to requests, build integration test suites, or use scripts to pass data between API requests, just to give you a few examples of what makes Postman Collections so useful.


Building a solid automated API testing strategy is the best way to ensure that your applications “work the same today as they did yesterday”. API testing allows you to build a solid framework for identifying defects at multiple layers of your application. Since API tests work at a much lower level than UI tests, you know that you will have consistency and the tests that you are building will last for a long time to come.

Ready to get started API testing but need to figure out whom to ask and what tool to use? Just click the below button to kick start of API Testing with Crowd4Test.

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