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The Smart Way to Do API Testing

Users today expect software applications to do wonderful things and interact with other applications in ways that would have seemed impossible not too long ago. To meet growing user expectations, companies of all sizes are shifting toward DevOps and embracing API-driven software architectures. By doing so, they are exposing themselves to a new kind of risk: API vulnerabilities.

In this article, we explain the importance of API testing for making sure that applications are ready to ship and our recommendations of three popular API testing tools that you can use to do API testing the smart way.

What is API testing?

As you may already know, API stands for Application Programming Interface. You can think of an API as a brain with many individual neurons that are activated by specific impulses. Any company can create an application that sends an impulse to a public API and receives a certain response. This enables seamless communication and information exchange between multiple software systems from multiple software companies.

Uber’s smartphone app is an excellent real-world example of how APIs are used by developers to integrate functionality developed by other companies. When you book a ride with Uber, the app itself doesn’t know how to calculate the route. Instead, it calls the Google Maps API and waits for an answer. The entire process is so seamless that, from the point of the user, it seems as if everything were happening right in the app.

What API testing aims to accomplish is to ensure that APIs and their integrations function in the most optimal manner possible and don’t contain any vulnerabilities that might help attackers compromise the server as well as the client.

There are several types of API testing:

  • Validation testing: High-level testing that seeks to answer whether the API actually meets the product requirements.
  • Functional testing: A broad methodology of testing multiple methods within the codebase to evaluate a slice of functionality in the system to find out whether the code is doing the right things.
  • Unit testing: Testing the functionality of individual operations to find out whether the code is doing things right.
  • Load testing: Testing of the API’s ability to handle edge use cases and perform under load. Load testing is often accomplished by reusing functional test cases.
  • Runtime error testing: A type of testing that looks for defects that are detected during the execution of the application.
  • Security testing: Tests what kind of authentication is required to access the API and looks for potential issues with the way the data is transmitted over the network.
  • Web UI testing: Used to validate GUI items in the context of end-to-end integration.
  • Fuzz-testing: Tests how the API handles massive amounts of purely random data.

API testing best practices

Considering that the API is what gives most modern applications and services their value, it’s easy to see why API testing has become such an important part of the software development process.

The good news is that it’s becoming increasingly easy to execute complex API tests thanks to modern API testing tools. But even the best tool in the world is only as good as its user, which is why it’s paramount to be aware of the best practices of API testing:

  • Tests may fail for a number of different reasons, including flawed functionality, environment failure, or a version discrepancy between the product and the test, so it’s necessary to write tests with debugging in mind.
  • Design your tests to run under different SUT (System Under Test) configurations. Flexible tests can better respond to real-world demands of product development, such as when a customer request leads to a version split.
  • You should always know what not to test. For example, it’s hardly ever a good idea to test the functionality of third-party applications, such as when working on a shopping application with an integrated payment processing gateway.
  • Always remember to add stress to the system when testing for invalid parameters and unforeseen problems. Your goal should be to optimize your API so that it fails gracefully no matter what you throw at it.
  • Automate whenever possible. In today’s fast-paced software development environment, API testing automation plays a more important role than ever before. In the next two years, the number of API testers who automated their tests is expected to grow by 30 percent, which can be in part attributed to the increased availability of excellent API testing tools.

Popular API testing tools

SoapUI

SoapUI is the world’s most popular automated API testing tool.

SoapUI is the world’s most popular automated API testing tool, covering everything from web service inspection to invoking to development to functional testing to load and compliance testing. The first version of SoapUI was released in 2005, and the tool has since then established itself as the go-to automated API testing solution of millions of professional API testers.

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

Postman

Postman is a complete API testing solution used by 5 million developers and more than 100,000 companies.

What started as a Chrome browser plugin is now a complete API testing solution used by 5 million developers and more than 100,000 companies around the world. What has convinced so many API testers to use Postman is its quick and dirty workflow that revolves around Postman Collections, which are executable API descriptions that let you group individual requests together and organize these requests into folders.

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.

Katalon Studio

Katalon Studio is a free, cross platform automation API testing tool.

Katalon Studio is a free, cross platform automation API testing tool built on top of open-source automation frameworks Selenium and Appium. It was first released in 2015, and it offers a unique keyword-driven approach to API testing and an easy-to-use user interface with a built-in integrated development environment (IDE).

Katalon Studio is available for Windows, macOS, and Linux, and there’s also a browser add-on for recording user actions in web applications and generating test scripts, called Katalon Recorder.

Conclusion

While there’s no one-size-fits-all approach to API testing, there are certain best practices that you should always keep in mind. Modern API testing tools make it easy to execute and automate complex API tests, and, in this article, we have listed our favorites to help you do API testing the smart way. For even more popular API testing tools, read this article.

Matt Warcholinski

Matt Warcholinski is the COO of Brainhub (a software house building awesome node.js web and mobile apps) who loves to build startups and play guitar.

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