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Application programming interface (API) testing is software testing that gauges whether developed APIs meet an application’s functionality, security, reliability, and performance expectations. When an application fails due to problems with the API it consumes, it has serious consequences for the users of the application.
For storage applications, failure could lead to compromised data and poor performance among others, and could be costly to fix in terms of money and reputation. Therefore, to protect and improve the application, and to better the experience of the users, it is important to test the APIs it consumes. Testing helps expose defects at an early stage as well as automating the process to cut costs associated with manual testing efforts.
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Benefits of API Testing Tools
Efficiency and reach of tests
Application programming interface tests are carried out at the fraction of the time a similar number of tests, such as graphical user interface tests, would take. As a result, the saved time can be used to iron out issues and increase overall efficiency. Since test cases are isolated and ready for use, testing is not dependent on multiple teams completing their work.
Lower mean time to resolution
The average time it takes to resolve failed application programming interface tests is reduced since these testing tools help pinpoint issues and flaws. The focus on application programming interface testing saves time that would be previously spent on prioritizing analyzing software builds and bugs.
Cost-effectiveness
Comparing automated graphical user interface testing and automated application programming interface testing, the latter is more cost-effective. Application programming interface testing requires less code, leading to quicker testing. This results in reduced testing costs. Furthermore, such testing tools reduce the need for manual testing, which also saves money.
Security and robustness
Application programming interface testing tools help in exposing and resolving vulnerabilities by subjecting software to extraordinary scenarios and conditions. Successfully pushing software to its boundaries in a controlled environment ensures software will not break in production. Vulnerabilities are also fixed to safeguard against malicious code and other threats.
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Comparison of API Testing Tools
Even though each mentioned application programming interface testing tool has its uniqueness, there are a few features that are common to most of them. For instance, all of them offer integration with continuous integration and continuous development (CI/CD) tools to improve development workflows.
These testing tools also allow users to write tests. Their focus is not only on programmers, but also non-programmers through the use of an easy-to-use graphical user interface and provision of automated API tests. The automated API tests are powered by the reusability offered by most of these tools. This reusability may be in the form of test suites, test cases, and/or code.
Most of the listed API testing tools can save you the time taken to run multiple instances of the same test through parameterization. Test parameterization features allow you to test multiple instances of a request by inserting variables in any section of the request.
| Tool | Test parameterization tools | Mocking | AI-powered automation | Automated and exploratory testing |
 Postman | Yes | Yes | No | Yes |
 SoapUI | Yes | Yes | No | No |
 Katalon Studio | Yes | No | No | Yes |
 Apigee | No | Yes | Yes | No |
 ACCELQ | Yes | No | Yes | No |
Top API Testing Tools
Postman
Postman, one of the top API development collaboration platforms, offers an API testing tool that simplifies the setting up of automated tests. Users can create tests and requests then aggregate them into one test sequence. Postman offers flexibility in managing test workflows through the use of Postman monitoring, the Postman app, or Postman’s command line tool called Newman.
Key Differentiators
- Exploratory and automated tests. Postman not only offers automated testing, but also simplifies exploratory testing. Exploratory testing is often thought to be at loggerheads with automated testing. However, it seeks to expose defects that other types of testing may fail to flag, therefore complementing the automated tests. Postman allows users to use pre-scripts to send asynchronous requests by executing logic in the background when sending multiple requests.
- Collaborative tools. Postman makes workflows social by offering teams the ability to comment on the documentation, maintain a single source of truth, and notify teammates of any changes through its workspace.
Cons: However, it is worth noting that the offering of Postman as a standalone app involves installing it locally. Users may experience longer load times with Postman interacting with large datasets and API responses.
SoapUI
SoapUI is one of the most popular API testing tools today. It is a java-based open-source tool for testing web services such as SOAP, RESTful, or HTTP-based services. As SoapUI is a free tool, it has a premium companion called ReadyAPI, which offers added API testing functionality.
Key Differentiators
- Code-free test environment. SoapUI offers a code-free test environment to simplify the creation of tests by running highly complex tests with drag-and-drop as well as point-and-click functionality.
- Data-driven testing. The premium companion of SoapUI (ReadyAPI) allows users to perform data-driven tests to simulate user interaction with APIs. ReadyAPI reads and loops test data from external sources such as databases, Excel, XML, and files.
- Auto mock creation. Users can mimic the behavior of web services in SoapUI before they are implemented. This allows users to test the services and prevent unnecessary expenses of building replicas of production systems. SoapUI automatically generates mock methods for the user.
Cons: Users may feel overwhelmed attempting to manage all open files within the main SoapUI window. It may also take new users some time to familiarize themselves with the interface as SoapUI may require experience on API testing to use it. SoapUI’s resource usage when carrying out a large number of tests may slow down your device.
Katalon Studio
Katalon Studio is a multifaceted API testing tool that both advanced testers and novice testers can feel right at home using. It is capable of combining UI and API services for environments such as Windows, Linux, and Mac OS. Katalon Studio was made to help users not only create but automate test scripts without having to code.
Key Differentiators
- Intuitive integration development environment (IDE). Katalon Studio’s IDE allows users to be more productive by auto-completing, auto-formatting, and inspecting code features. It also offers already built and customizable code templates. This optimizes the scripting and debugging processes for users. It also makes it easy to maintain API tests.
- Data-driven testing. Like SoapUI, Katalon Studio also allows users to carry out data-driven testing by reading inputs from both internal and external files.
Cons: Katalon Studio supports only one scripting language, known as Groovy, which is in the Java programming language family. More supported languages would appeal to the preferences of more users.
Even though Katalon Studio has some open-source components such as built-in Keywords, Katalon Studio is not open source. As a result, its community has a smaller number of developers.
Apigee
Powered by JavaScript, Apigee is a cross-cloud full-lifecycle API management platform that allows users to measure and test API performance through API traffic, error rates, and response time. It is useful to complex digital businesses since it can handle APIs with large amounts of data.
Key Differentiators
- Cross-cloud API testing. Since it’s cross-cloud, users have the flexibility to choose where to host their APIs, whether on Google Cloud, on-premises, or hybrid. Apigee allows developers and testers the freedom to test their APIs on public, private, or hybrid clouds.
- Easy creation of API proxies. You can create API proxies to protect your app-facing API from backend modifications to code. Apigee achieves this by detaching the app-facing API from backend services.
- AI-powered automation. Apigee uses artificial intelligence to ensure APIs are performing as required. Through just a few clicks, users can easily diagnose their API problems. AI-powered API monitoring also offers real-time anomaly detection.
Con: Apigee does not have a free option. There’s an evaluation plan that provides a handful of features but expires after 60 days. In comparison to similar tools, Apigee may end up being pricier.
ACCELQ
ACCELQ is an AI-powered test automation platform that uses natural language programming to enable the creation of test logic in English instead of lines of code. It uses application abstraction to enable test planning, design, creation, and execution to be carried out at any stage of development. As a result, users end up spending less on maintaining tests.
Key Differentiators
- Zero code automation of API testing on the cloud. ACCELQ is a cloud-based API testing tool that offers users the power to automate API testing without authoring a single line of code. It is of benefit to development teams of all sizes as they can accelerate their testing workflows.
- Automation of self-healing powered by AI. ACCELQ intelligently adapts to unanticipated application changes to ensure reliable test execution. ACCELQ also uses AI to auto-generate test cases.
Con: Considering there exist free and open-source API testing tools, ACCELQ’s pricing, starting at $70 a month, is costly in comparison.
Choosing the Best API Testing Tool
To choose the right API testing tool for you, it is important to determine which features are a must for your software development workflows. To do this, you have to consider the factors that would greatly transform your workflows. For instance, would an open-source tool serve you better? Or would you rather subscribe to a premium tool? Is your team full of software developers? If yes, do the tools available cover their languages of choice? Or is your team non-technical? Would you prefer zero-code workflows? Are you seeking a tool that offers collaborative functionality? Answering such questions would put you in an informed position to select the best tool for you and your team.
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