API Testing: benefits, types, tools and more

Software development now revolves around APIs, which link and transmit data and functionality between many systems and applications. Fortunately, testing these can significantly increase the effectiveness of any testing procedure in general and enable you to produce software more quickly than ever.

API testing has gained more recognition during the last five years. It is a necessary tool for just about any products testing team, utilized for everything from basic tasks like loading images to major ones like processing payments.

What is an API?

APIs are essentially a collection of methods and functions which enable the development of apps. API serves as the messenger between you and the service provider, taking your request and responding with the result. In simple terms, they serve as a sort of middleman between various software systems. They enable communication between two unconnected programs. They gain access to the information and functions of different programs or operating systems. 

By offering all the necessary building elements, effective APIs simplify it for programmers to construct computer programs. Besides, they work with various formats like XML, JSON, plain texts, and HTTP. Because you may combine and reuse APIs indefinitely to create new services.

Software developers can design APIs using a variety of architectures, but REST or SOAP is the most prevalent. REST APIs adhere to REST standards and transports data from the server to a client. SOAP APIs use XML to encrypt data. The SOAP specification is very specific about the format and content requirements for messages. 

What is API testing?

API testing involves sending requests to an API and watching and checking for responses to make sure it behaves as intended. API testing is an integral element of the API development lifecycle and tends to evaluate the usability, dependability, efficiency, and security of an API. Unlike unit testing and user interface testing, API testing concentrates on the functionality of the application rather than its separate parts or how it appears to the user. This is often referred to as UI testing. A brief on the difference between API vs. UI testing is as follows.

API vs. UI testing

In API testing, users utilize software that makes requests to the API, retrieves output, and records the response of a system rather than the user inputs and outputs. API testing primarily focuses on the business logic of the software and does not focus on how an application looks and feels. However, while using a graphical user interface (GUI), user interface testing finds flaws in products and software. By testing displays and elements like menus, buttons, and icons, the UI tests aim to make sure the functionality of software applications functions according to its standards.

Types of API tests

Now that we went through what is API testing, let’s get to a couple of API testing types.

Integration test

Integration tests or String tests (or Thread Tests) test if software components are logically connected and examined as a unit. Multiple software components created by various programmers make up a typical piece of software. This degree of testing’s objective is to find issues with how various software components communicate when they are together. 

Performance test

Performance testing is an approach for evaluating software that measures a software application’s responsiveness, scalability, stability, and resource utilization in response to a certain workload. It mostly locates and fixes software application performance issues.

Before the software is released to the market, it reveals what has to be changed. Without performance testing, the product may experience problems including slow performance when numerous users are using it at once.

Load test

The functionality of a software program under different loads is tested during load testing. It’s a non-functional testing procedure that happens under predetermined expected traffic. Before deployment, load testing aims to eliminate performance bottlenecks and guarantee the stability and efficient operation of software applications.

Dynamic Security test

Security testing looks out for system faults and determines if the program’s resources and data are protected from hackers. It assures that the software remains safe from any dangers or threats that could result in harm. Any system’s security testing aims to identify any potential flaws and weaknesses that could lead to the loss of data or the organization’s reputation.

A dynamic API security test replicates an actual attack and identifies risks that were generated by both the code the development team wrote and its reliance on open-source libraries.

Fuzz test

API fuzz testing is an automatic test technique that involves feeding the API with incorrect information to check for crashes or problems. Fuzz testing finds any hidden problems and flaws.

Fuzzing is a technique that hackers regularly use to find software bugs despite having the source code to work with. Hackers can leverage vulnerabilities they’ve found to attack the API with DDoS and inject SQL, among other exploits.

Fuzz testing does not, however, give a complete view of the API’s security status. More API security testing is required to provide the maximum level of security for the APIs.

Validation test

A validation test confirms if the software that has gone through testing and development meets the needs of the user. Detail-oriented testing must be done on the requirement specification logic or scenarios. An application’s essential features must all be evaluated in this area. A tester determines whether the outcomes of the test execution are consistent with the information in the requirement specification.

Interoperability test

Software testing of this kind determines whether the program can communicate with other programs and computer systems. Interoperability tests make sure that there are no compatibility problems in the software product’s ability to interact with other parts of the software.

Interoperability testing, in other terms, entails demonstrating that the end-to-end functioning of bidirectional communication systems complies with the requirements. For instance, testing for interoperability among tablets and smartphones verifies Bluetooth data transfer.

Runtime/Error test

This sort of testing is concerned with how the API operates, in particular with the overall outcomes of applying the API code. This method focuses on one of the following: error detection, monitoring, execution errors, or resource leakage. Runtime error detection can pinpoint the main reasons why an application crashes, runs poorly or behaves inexplicably by identifying errors that only show up during runtime (for instance, file overwrites).

Connection timeout test

If a service takes longer than a certain time to answer a call, timeouts occur. This time is a configuration and can change depending on the platform. If a timeout occurs, the response will contain information about it along with the 500 error status code. There can be many causes for timeouts including having too much data in the call or having a problem with the network or service.

We may need to test the application’s fail-safe behaviour, which is how it acts when external systems fail to reply within the specified time frame. Therefore, it is advisable to make use of timeout-related tests.

API testing tools

API automation testing is essential to effective testing. Your development team needs automation if it wants to become more productive. With the help of API automation testing tools, you can easily bypass the difficult and error-prone process of manual testing.

Additionally, you may frequently combine an API automation testing tool with your workflow for continuous integration. This integration is a great option for enhancing the quality of your code by spotting defects during the software development lifecycle. 

Postman

You can use Postman to supervise the API, build automated tests, carry out debugging, and send out requests. Postman has currently extended its features to Windows and macOS. Postman uses highly innovative features in its latest version to improve testing, collaboration, integrations, and also API governance and security. It’s a free tool but there are paid packages with advanced features. 

Playwright

Playwright can gain access to your application’s REST API. There are occasions when you may wish to use Node.js to send requests straight to the server rather than loading a webpage and executing Javascript code on it. This can be to test your server API, set up the server side before accessing an application, or verify your server conditions after executing specific browser-based activities. Playwright’s APIRequestContext methods will be useful to accomplish all of that.

SoapUI

SoapUI allows for the execution of tests on both SOAP APIs and RESTful web services. Since it enables users to design complicated scenarios and further facilitates asynchronous testing, it is frequently one of the chosen tools by testers. It also sets out for its excellent data-driven testing and user-friendliness. One of SoapUI’s two packages is free, while the other is not. The free option is comparatively simple to use, and testers can reuse scripts. The paid option supports native CI/CD integrations, native data extraction, and custom code creation.

Assertible

Assertible is generally acknowledged by developers and testers as one of the best API testing solutions because of its dependability. It allows API tests at every stage from continuous integration through the delivery pipeline. Assertible offers its users many helpful features. It is compatible with GitHub integration. Assertible also uses readymade assertions to validate HTTP replies.

Assertible offers a free plan to test and learn how to use it. Apart from that, it offers various other paid plans.

Apigee

JavaScript-based Apigee is an intriguing cross-cloud API testing tool that gives developers and testers access to its functionalities using a variety of editing features. This tool is appropriate for APIs that contain a lot of data, making it the perfect choice for robust and intricate digital enterprises. By examining API volume, response rates, and possible error rates, it quickly spots problems that are impairing performance. 

Apigee offers a free trial that enables you to test it out. After that, companies and testers must pick the best package to keep utilizing it. The trial, Standard, Enterprise, and Enterprise Plus are the currently available packages.

Katalon

Katalon is available for online, desktop, and mobile apps as well as APIs. It offers numerous customization capabilities and commands.  In addition, Katalon supports CI/CD integrations, adopts a data-driven methodology, and gives testers access to automation and exploratory testing. Its major benefit is that it is not difficult to use, making it appropriate even for non-techies. 

As for pricing, Katalon provides a free plan and a premium plan with more advanced functionality and exclusive plugins. The Ultimate plan with mostly unlimited features is available only for enterprises. 

Karate DSL

Karate DSL is a single framework for API automation testing, mocks, load testing, and performance testing. The knowledge of coding is not required for users to use this application. However, it helps to have a basic understanding of HTTP, XML, XPath, and JsonPath.

Rest Assured

Rest Assured makes it simple to test REST services. It is a Java-specific and open-source tool created to simplify REST testing. Users won’t have to start from scratch when using built-in functionalities. They also don’t have to be familiar with HTTP. The most recent version also added better CSFR support. However, while the tool is free, the solutions are not.

API Fortress

API Fortress enables developing and automating performance and functional testing easier. Their features include continuous API stimulation by plug-and-play, web services support, and allows for team collaborations. It is therefore the most effective SOAP and REST monitoring tool. 

Benefits of API testing

The following are some of the benefits of API testing. 

Reduces testing costs

The quicker implementation of API automation testing results in more effective resource usage and cheaper overall testing expenses. Before any UI testing and even before the business logic is established, API tests can be run. Thus, it will aid in early problem identification. Early detection decreases the price of application updates and makes fixing the problem less expensive.

Faster bug fixes

You’ll be able to see straight away whether the results are positive or negative because API testing works rapidly to deliver a solution. This can aid in troubleshooting earlier in the system’s development, enabling effective bug discovery and elimination.

Quicker release

UI testing is known for delaying the delivery of products. The quicker option, though, which can save you approximately eight hours, is API testing. You now can focus on other crucial elements of software development.

Understands any programming language

Any languages are suitable for testing APIs because data is sent using the XML and JSON standards. Therefore, it doesn’t matter whether you prefer Java, JavaScript, or Python.

Integration with UI tests

Fully integrable tests are achievable with API testing. This is particularly useful if you intend to test your UI after testing your API. For instance, simple integration would make it possible to add new users to the application before a UI test begins.

Conclusion

API makes up functions of a business logic layer. If an API is not properly tested, both the API application and the client application may have issues. This test is crucial in software engineering. Therefore, it is important to fully understand what is API testing, the different types of API testing, the existing API automation testing tools, and more importantly the benefits of API testing.