What is API Testing? Types and Benefits

Before we discuss API testing, it’s important to understand what an API is. Acronym for Application Programming Interface, APIs can be referred to as the middlemen that connect one software system to another or, in other words, allow two applications to talk to each other. Whatever actions you perform inside an app, there’s a specific API that makes the back and forth communication possible. For every action you perform, the application sends that data to the server (backend), which then reads and interprets that data, and sends it back to the user in a readable format (in the frontend); all this happens via an API.

This is as simple as ordering food in a restaurant. You call the waiter and tell him what you need. He then passes the information to the kitchen staff (chefs) who prepare your food. Once cooked and ready, the waiter brings it to you. Now understanding it from the application’s point of view, the waiter represents the API. Why? Because he is the one who is connecting you with the chefs. He is sending the order (data) to the kitchen staff (backend). The chef takes your order, prepares it, and asks the waiter to serve it to you. The cooked food that you receive at your table represents the front-end.

We also made a post explaining this on our LinkedIn page.

https://www.linkedin.com/feed/update/urn:li:activity:6848519753561178112

Now, let’s understand what API testing is.

What is API Testing?

API testing is a software testing practice used to validate APIs. It’s a part of Integration testing. The objective of API testing is to test the functionality, reliability, performance, and security of the programming interfaces. This testing method uses software to send calls to the API rather than standard user inputs and outputs, and then the system’s response is noted down.

Generally, there are three layers in an application- the presentation layer, the business layer, and the database layer. The primary focus of the API tests is on the business layer in which business logic processing is carried out and all transactions between the presentation layer and database layer occur.

Why Does API Testing Matter?

UI tests are considered inefficient for validating API functionalities and usually do not cover every aspect of backend testing. This could leave bugs within the servers or unit levels that can result in a delayed product release as one would have to rewrite large amounts of code.

APIs have to deal with the processing of most of the traffic, and if they fail in some unexpected ways, the consequences might be drastic. Failure of an API could lead to services not being available, processes not working as expected, and it could even allow access to sensitive objects and data.

Benefits of API Testing

There are scads of benefits of performing API testing, such as-

1. Testing can be done early

For API testing, you don’t need to wait for GUI testing. It is GUI-independent and thus can be performed prior to it. This is because the API components are often developed before the UI ones.

Early testing allows for testing the app’s core functionalities that help evaluate its build strength. Moreover, it enables faster feedback and better team productivity.

2. Faster testing, faster release

300 API tests can be run in a 3-minute span whereas the same number of UI tests would take approximately 30 hours. This means more bugs can be found and fixed in less time. API testing saves up to eight hours compared to UI testing, and thus allows the software development team to release the product faster.

Also, the code required for API test automation is comparatively less than what’s required for automated GUI tests, thus resulting in faster testing and a lower overall cost.

3. Language-independent

Another benefit of doing API testing is that API tests are language-independent, which means any language can be used for API test automation. Data is exchanged through JSON or XML formats, which help make the process faster and more stable. There are in-built libraries as well for data comparison using these formats.

Types of API Testing

API testing involves different types of tests performed at different stages of application development. Let’s take a look at a few.

1. Validation Testing

Validation testing is usually performed at the end of the development process (sometimes during the process too) specifically after the verification completion of API’s constituents and functions. This is done to verify that the software meets the specified requirements when deployed in an appropriate environment.

During validation testing, the focus remains on three important aspects- Product, Behaviour, and Efficiency. For the first part, it is checked whether a correct product has been built or not. Is the API itself the correct product for the provided issue?

For the behavior aspect, a few questions are addressed such as is the API accessing the correct data, is it storing that data correctly, or is it accessing too much data?

The efficiency aspect addresses questions like- Is the API the most accurate, optimized, and efficient method of doing what is required?

2. Functional Testing

Functional testing is nothing but testing specific functions within the codebase. These functions are basically specific scenarios made to ensure that the API functions within the expected parameters, and can handle errors well when results are outside of the expected parameters.

3. UI Testing

UI testing is about testing the user interface for your API and its constituents. It is concerned with the functioning of the UI. In many ways, it is less of a test of the API but more of the interface that ties into the API and the developer’s experience of using that API. Although it doesn’t directly test the API in terms of the codebase, it does provide a generalized view of the health, usability, and efficiency of both front-end and back-end.

4. Runtime and error detection

This API testing type is concerned with the actual running of the API. While most of the other API tests are primarily concerned with the result obtained after the API implementation in an environment or scenario, this particular test is concerned with the universal results of utilizing the codebase.

5. Security, Penetration, and Fuzz testing

Though Security testing, Penetration testing, and Fuzz testing are different in their own ways, they all are a part of a greater security auditing process. These types of tests focus on securing the API from external threats.

Security testing focuses on the validation of encryption methodologies and the design of the access control solution. The second step of the overall process, i.e. penetration testing, checks for API threats in case someone attacks the API or has a working knowledge of it. Lastly, in fuzz testing, a vast amount of random data, often referred to as “noise” or “fuzz,” is forcibly put into the system in order to attempt a forced crash, overflow, or other negative behavior. This is done to test the API at its absolute limits, to test how it would behave in what we would call a worst-case scenario

Final Thoughts

API testing is an indispensable part of software testing. If API isn’t tested properly, it may cause certain problems in the software application. Also, keep in mind that it’s not just the user-facing functionality that needs to be tested, but APIs are also integrated with other services or third-party providers. So we can’t afford to leave them untested.