Review of popular tools for testing API

The concept of API

The interest in API testing has grown significantly in recent years. It is caused by the increase in the number of web and mobile applications, as well as the separation of the server side and the user interface.

Before moving on to API testing tools, let's recall what an API means.

API (Application Programming Interface) is an interface for communication between software components.

Functional testing is performed on the user interface side. In contrast, API testing allows bypassing the visual interface and directly connecting to the application or website by sending requests to the server.

Here's how it works:

1. A client makes a request when accessing a resource.
2. The request is sent to the server capable of fulfilling this request.
3. The server finds the required resource and responds to the client.

Many tools exist to directly test API requests, but we'll review just a few of them: Postman, SoapUI, and Katalon Studio. This article will introduce you to the main features of each of these tools.

Postman

Postman is a client used for automated API testing that originally started as a plugin for the Chrome browser but later became available on desktops for Windows, Linux, and Mac. However, automation is not the main purpose of using this application. It is also suitable for exploratory testing. Postman can also be an effective tool for developers to create and test APIs.

The app allows configuring the necessary headers and cookie requests that meet the requirements of the tested API and checking the received response.

The main advantages of the tool:

• a well-implemented interface, because of which it is easy to understand the functions and use them for tests;
• allows sharing the results with colleagues, since it provides the ability to save all requests and answers and send them to other users;
• integration with popular formats such as Swagger, RAML, and others;
• does not require learning a new programming language. 

Postman has both free and paid versions. Paid versions provide more support and additional features. The free version is enough for simple API testing.

SoapUI

SoapUI is another popular tool for API testing. This tool is most often recommended for testing API since it was developed for this purpose. There are two different versions of this tool: a free open-source version and a Pro version. The free version allows modifying the code, while the Pro version has a more user-friendly interface and additional functionality, including a form editor and SQL query editor. 

SoapUI has a good test generation system, the recorded scripts can be reused, and there is also a well-implemented toolkit for testing data with access to files or a database.

The advantages of the paid version:

• the ability to work with external data (XML, Groovy, Excel);
• test coverage - the Pro version allows collecting statistics on the functionality of the product that has already been tested or is still in the process;
• supporting multiple test environments, for example, Dev, QA, Pre-Prod and others;
• reporting – the ability to customize reports and generate them in different formats, for example, PDF, HTML, Word, Excel;
• security testing – both versions of SoapUI allow conducting testing, while only the Pro version provides access to a vulnerability scanner;
• support – the Pro version provides exclusive support from the standard one on the online forum.

Katalon Studio

Katalon studio – is a free test automation tool from Katalon Studio company with a graphic interface. It can also be used for API testing. The ability to merge UI and Business levels (API/Web services) for different operating systems is a main benefit of the product.

The main advantages of the tool:

• free software, but without open source;
• supports both SOAP and REST API;
• easy to install and use;
• low entry threshold;
• has the functionality to test web services and REST API;
• allows sharing recorded tests with colleagues;
• uses a built-in keyword search system to create scripts.

So which tool is better to choose?

There is no certain answer to this question. The same Postman is easier to use and good for exploratory testing. If there is a need to automate the testing process then the choice falls on SoapUI. Also, SoapUI provides a richer interface that makes it possible to make more different settings during the testing process.