What Is API Testing? Definition, Importance, and Types

API Testing

API or Application Programming Interface is the connecting bridge or the medium of communication and data exchange between two separate software systems. It is considered the middle layer of the software applications’ three-layer structure i.e. the following -

  • The database layer.
  • A service layer or the API layer.
  • A presentation layer or the user interface (UI) layer.

API is an extremely significant part of building, running, and maintaining software so, you must be aware of everything about it and why it is so important to test them.

What Is An API?

API or Application Programming Interface is the middleware that enables two layers of an application to communicate for performing operations and allows different applications to collaborate for executing tasks that you want them to perform. For example, when you search for restaurants, ATMs, gas stations, or anything else near you, it apparently looks like Google is showing a list with the places in an order of the closest ones to the ones at higher distances from you. But, you must know that Google Maps API and those places’ websites’ API are the ones working behind the scenes to get you the results.

API may be a commonly heard word in the tech world but sometimes people don’t know much about it. So, after we looked at a brief introduction of it, it’s time to move toward API testing, the main topic of today’s discussion.

What Is API Testing?

API testing is the part of software testing that ensures that an API is achieving and maintaining its maximum performance, functionality, security, and reliability. These tests are extremely crucial because being the middle layer of software applications, testing an API is a remarkably efficient approach for ensuring the best performance throughout the entire operation performed by the app. These tests are performed either directly or as part of integration testing, another method of testing the combinations of software modules or better known as units. The commonly followed way of performing these tests is making requests to one or more API endpoints and comparing the response with expected results. These tests are concerned with analyzing the business logic and checking the application’s security as well as data responses. Now, let’s see more about this important form of test in the further sections of this article.

Why Is API Testing Important?

The reasons that make API testing an unavoidable part of your software testing process are mentioned below.

  • Though you know that UI tests cover an application’s visual aspects that users directly interact with, those tests are often unable to test the functionality of the API service and other back-end aspects of the application. Hence, not performing API tests and solely relying on UI tests can lead to numerous bugs left within the server or unit levels. As a result, the release of the product will get delayed and you will need to rewrite huge chunks of code.
  • Nowadays, a lot of companies use microservices for their software applications. The motive behind using microservices is to avoid the shutdown of all the parts of an application when updates are getting implemented on any one part. Microservices enable every part of the application to have its own data store and specific commands to interact with that data store. So, if the deployment of an update is going on in one part of the application, other parts can function normally. Now, the point is that most microservices use APIs, and as using microservices is so efficient, most businesses are adopting it. Hence, API testing is an essential requirement for most tech businesses.
  • API testing allows you to perform tests earlier even if the UI is not ready. These tests ensure that any request that is not producing the appropriate value at the server layer, will not be present in the UI layer and mess that up too. As a result, developers become capable of correcting at least half of the bugs before they become more serious problems. Executing API tests allows testers to make requests that are mostly impossible through the UI and to easily explore security flaws.
  • API tests have even more importance in agile software development methodologies. One of the primary characteristics of agile methodologies is working in small sprints that are eventually based on quick feedback from the tests. Now, unit tests and API tests are capable of providing faster feedback than graphical user interface (GUI) tests. Hence, API tests help developers to get quick feedback and act faster to maintain the pace in agile software development processes.

Benefits of API Testing

The benefits or advantages of performing API tests are -

The Tests Are Language-independent

These tests need data to be exchanged via XML and JSON formats allowing the use of any language for test automation. Being well-structured, XML and JSON make the verification process fast and stable. There are also built-in libraries available for comparing data using these data formats. Hence, a good part is that exchanging data via XML and JSON formats makes API tests language-independent.

The Tests Does Not Depend On GUI Tests

As we previously mentioned, API tests are normally performed before GUI tests and that earlier testing approach leads the testing team to get faster feedback and achieve better productivity. In API tests, as soon as the logic is designed, the tests can be created and executed to check the correctness of responses and databases. As a result, the testing team becomes capable of detecting the bugs quite early and those bugs do not move to the UI layer. Hence, these tests do not depend on the GUI and are far less complicated.

Easier Test Maintenance

To know about the advantages of API tests in terms of test maintenance, you need to compare them with UI tests. User interfaces are highly dynamic and they are constantly changing & moving around depending on the wide range of devices, screen types, browsers, etc. used by the users. Hence, in UI tests, the test codes need to be constantly updated to keep up with the applications’ code in production. On the other hand, APIs change in a more controlled manner and with quite less frequency. API definition files like OpenAPI specification allow you to refactor the tests within a glimpse. All these quick and simple movements enable you to easily maintain the API tests.

Higher Test Coverage

It is always a best practice to test almost every portion of your application, but due to the huge codebases, the complexity of tech products, and the pressure of meeting deadlines, companies often have to release products without testing large portions of the codebase. Many tests are so complex and time-consuming that companies become left without any option to leave them unexecuted. However, such low test coverage can lead your products to fail repeatedly and will create a bad impression of your business.

API/Web services have their specifications that help the testers to create highly efficient automated test scripts for the API tests including functional & non-functional testing. As a result, you become able to achieve a higher test coverage in less time.

Faster Time To Market

As you saw in the previous point, API tests take significantly less time than time-consuming tests like UI tests. For example, while 300 UI tests may take around 30 hours to complete, 300 automated API tests can be run in around 3 minutes. Now, running such important tests so fast can help you detect bugs quicker and debug them as soon as possible. As a result, you can release your product much faster than expected.

Types of API Testing

Based on various parameters, API testing can be categorized into a few different types. We have jotted down some important types below.

Functional Testing

Functional tests are a crucial part of the overall testing process. These tests ensure that different parts of the system are functioning properly. In terms of API testing, these tests check that the API functions are fulfilling the expectations within the planned parameters.

Validation Testing

As the name suggests, validation tests are all about validating the correctness of the development process, and that can be properly done during the final phase of development. These tests check the correctness of various aspects of a product including its behavior and efficiency. Hence, this form of API testing is all about validating that the overall development process is going as planned.

UI Testing

Although UI tests are often compared with API tests as different forms of testing, user interface tests also check the APIs and other integral parts of them. UI tests put more focus on the interface that ties into the API rather than the API tests doing the same. Though according to the codebase aspects, UI tests are not specific tests for APIs, they are still very useful to ensure the best levels of the health, usability, and efficiency of an application’s front and back ends.

Load Testing

The objective of executing load tests is to check if the application performs as expected with both normal and peak load levels. Hence, these tests are performed when a unit or the whole application is developed. Then you have the codebase before you, and you can plan & create tests to check if the codes and APIs are working properly.

Security Testing

Security testing is a highly important form of API testing because it lets you know if the API implementation for your application is secure from external threats. These tests perform tasks like validating encryption methodologies and the design of the API access control. So, from the importance of the aspects that they ensure security, you can easily understand how essential these tests are. On top of that, these tests are also responsible for user rights management and authorization validation.

Runtime and Error Detection

This is a form of test that actually focuses on the running of APIs. They are more concerned about the universal results of utilizing the API codebase. They check the runtime of the APIs and detect the errors if there are any. The main things that these tests look at are execution errors, runtime monitoring, error detection, and resource leaks.

Performance Testing

These are the tests that look after the performance of the APIs. These tests help you to implement the shift-left method in the entire software testing process. Before the dominance of the API-based performance testing tools, load testing was very difficult to include in the CI/CD environment. Efficient performance testing tools like RestAPI let any member of the team embed performance tests in their CI/CD pipeline.

Penetration Testing

These tests are sometimes considered the second test in the auditing process. These tests need users with limited knowledge of APIs to try assessing the threat from outside. The main focus of these tests is always on functions, processes, resources, or aiming at the entire API and its components. So, you can easily figure out how important these tests are.

Fuzz Testing

This form of API test is another massive step in the security audit process. These tests are named in that way because they involve large amounts of random data (which is known as “noise” or “fuzz”). These tests need that fuzz to be put into the system to detect any forced crashes or negative behaviors. This is an efficient testing technique that ensures that the API is capable of handling the “worst-case scenarios”.

Why PreFlight Is The Best Choice For API Testing

From all the discussion, you clearly have got an idea of what API testing is and why they are so important for successfully running a tech business. Now, you might also have figured out how time-consuming and error-prone it becomes to perform those crucial tests manually. Hence, the best practice is always to automate them using an advanced test automation tool, and Preflight is the best choice for you there.

This simple yet extremely powerful and efficient browser extension is capable of fulfilling all your API testing needs along with all other forms of tests. It provides you with truly remarkable features like -

  • Advanced AI-based technologies like context awareness that uses computer vision, OCR, etc.
  • Amazing cross-browser and cross-platform support across a wide range of devices with different screen sizes.
  • Super-easy click, drag & drop test creation, running, and management.
  • Auto-recording and playback feature to rerun and analyze the tests.
  • Options to integrate with all popular CI/CD, version control, and product management tools.

These are some of the most important features that you can get from this tool. There are a lot more to these and you can get to know them in-depth from the article “10 Amazing Software Testing Benefits From Preflight In 2022”. And, the best part is that such an awesome testing experience is offered to you at truly affordable prices. So, drop the worries about test automation and sign up with us.

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