What is API Testing? | Definition, Benefits, Tips, Tools, and Types

API: Application Programming Interface. With a set of protocols, it helps you to communicate between two apps or components or computer hardware. Before getting more knowledge about API, we should understand what is API testing and Why is it becoming the foundation of any software application?

API testing is a huge topic or process. It ensures that an application’s efficiency is maximized. With the correct strategies, tips, and tools – you can optimize the full process of API testing. Because there are so many types of API testing, it’s important to start with an understanding of many API testing. We’ll look at the many types of API testing, as well as a few API testing tools in this post. 


What is API Testing?

Definition of API Testing: API is the layer that sits between the user interface (UI) and the database layer in software application development. It allows data and communication to flow from one software system to another. It is a type of software testing that examines APIs directly, including their functionality, dependability, performance, and security. API testing, which is a subset of integration testing, checks the logic of the build architecture in a short period.

API may be used for a variety of reasons.

  • Software Libraries
  • Computer Hardware
  • Computer Operating System
  • Web-based applications
  • Database System


Benefits of API testing

Benefits of API testing - Infographic


Types of API Testing

1. Validation Testing

Validation testing is one of the ultimate processes in the development process and is critical. It analyzes the features of the product, behavior, and efficiency. Validation testing is viewed as a guarantee of proper development.

2. UI testing

A test of the user interface for the API and other important parts is referred to as UI testing. It is more concerned with the interface that connects to the API testing than with the API itself. Although UI testing is not a specific test of API in terms of the codebase, this technique still summarizes the health, usability, and efficiency of the app’s front and back ends.

3. Load Testing

Load testing is ‌done after Validation & UI testing. This technique verifies that the theoretical solutions operate as expected. This testing checks your application performance in both (normal and peak) conditions.

4. Fuzz Testing

Another phase in the security audit process is fuzz testing. Fuzz testing involves feeding the system a large amount of random data (referred to as “noise” or “fuzz”) to discover any induced crashes or bad behavior. This approach evaluates the “worst-case scenario” of API boundaries.

5. Runtime and Error Detection

This test type is related to the actual operation of the API. It is especially the general result of using the API codebase. Monitoring, execution problems, resource leakage, and error detection are all parts of this method.

6. Security Testing

This procedure protects the API implementation from outside attackers. Additional phases in security testing include validation of encryption technologies and the architecture of the API access control. It also supports authorization validation and user rights management.

7. Functional Testing

Functional Testing has features that include the performance of specific circumstances to ensure that API functions are properly managed within set parameters.

8. Penetration Testing

The final experiment in the auditing process is penetration testing. Users with minimal API understanding will attempt to analyze the danger vector from the outside in terms of functions, resources, processes, or the complete API and its components in this scenario.


Why is API Testing important?

1. Easy in Testing

Once the logic is established, you can easily develop test cases to evaluate the validity of the response and data. 

2. Simple in Maintenance

Because it is accessible from multiple browsers, devices, and screen orientations, the UI must continually alter, which is unstable, but the API does not face similar difficulties.

3. Resolution in Less Time

When an API test fails, it is easy to locate the fault since we already know where the system went wrong, which allows us to swiftly repair the issue.

4. Shorter time for Speed and Coverage Test

While UI testing may take longer, API tests provide findings in a shorter time while also having the potential to solve them quickly.


API Testing Tools

API Testing Tools

There were very few API testing tools in the past, but more have lately appeared on the market. Each API tool has its own set of functionality. Here are some well-known API testing tools:

1. Katalon Studio

It allows users to do API tests even if they have no prior knowledge. It supports much REST and delivers full report findings.

2. Apigee

It is one of the cross-cloud technologies for enabling the deployment of APIs and creating proxies for them. 

3. SoapUI

It is the most prevalent around the world. It may be used to rapidly and efficiently test REST and SOAP APIs. Apple, Microsoft, and Oracle are among the many leading brands that use them.

4. Postman

It’s a Google Chrome plugin that’s used to test all current web services APIs. It also helps in creating Boolean tests and the collection of REST requests for subsequent use.

5. Apigee

It’s one of the cross-cloud technologies for enabling API deployment and proxy creation. 

6. Tricentis Tosca

It’s an excellent solution for web services APIs; it supports several web protocols and is integrated with the DevOps agile cycle.



Here are some benefits for API testing to assist you in getting more professional tests and results:

1. Begin with simple, useful APIs

Beginning with modest inputs such as login API might open the door to API functions since it first provides an API environment.

2. Check the API output’s status

Recognize the ‌status code response to determine if you succeeded or failed the worldwide five-star criteria.

3. Know requirements

This will help in the establishment of a stronger validation strategy for specific data or APIs.

4. Implementing positive and negative tests

To ensure that the API is up to date,  This will help ensure that the input is received correctly and that the outputs are as expected.

5. Choose the best verification methods

To support the validation, this type of API response body content can be ‌plain text or an XML document.



APIs add value to the “smartness” in our phones. It is a set of functions or methods that define the business data model. 

In other terms, the API (application program interface) is a collection of protocols, procedures, routines, and tools that aid in the development of key software applications. It adds value to an application and aids in the streamlining of business operations.

API testing is required since it would be difficult to ask your customer to accept an application if it did not perform properly and efficiently. When you comprehend the scale of the internet of things, you will immediately realize how critical APIs are for tech-based firms and business transformation. API testing has become the hard concept in the chain of software & QA testing to ensure that digital lifestyles will work smoothly.

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