Table of contents
1.
Introduction
2.
What is an API?
3.
What is API testing?
4.
Why should we do API Testing?
5.
How to Perform API Testing? 
5.1.
1. Test environment setup:
5.2.
2. Application data integration:
5.3.
3. API test specification:
5.4.
4. Test execution and reporting:
6.
Types of API Testing
6.1.
1. Functional Testing:
6.2.
2. Reliability Testing: 
6.3.
3. Load Testing: 
6.4.
4. Stress Testing: 
6.5.
5. Security Testing: 
6.6.
6. Integration Testing: 
6.7.
7. UI Testing:
6.8.
8. Penetration Testing:
6.9.
9. Validation Testing:
7.
List of Popular API Testing Tools
8.
Challenges of API Testing
9.
FAQs
10.
Key Takeaways
Last Updated: Mar 27, 2024
Career growth poll
Do you think IIT Guwahati certified course can help you in your career?

Introduction

Have you ever wondered how websites accurately get information from the backend server, and the changes you make in the UI are updated in the backend? There must be a medium that sends and receives data from UI and the server. Let's go further into this article to know what that medium or software is and how it works.

Recommended Topic, Locators in Selenium

What is an API?

API - Application Programming Interface is an intermediate software that helps communication between UI and backend. It is a set of functions that allow the creation of applications that access data and other features of other applications, services, or operating systems. In general, APIs define the rules that programmers/developers must follow to interact with a programming language, a software library, or any software.

Every time you use an Instant messaging app to send a message, you're doing it using an API. The working of API is explained below, which helps us understand what an API does to process our data requests.

What is API testing?

API testing is software type testing, where an API is tested to check whether it exhibits expected functionality, performance, reliability, and security. In other words, the API tests validate an API. It reveals any bugs, inconsistencies if present in the API. Instead of any standard input given by the user and outputs in API testing, we use software to invoke or call API and get the result. 

API automation testing requires an application that interacts with the API. To test the API, we need to:

  1. Use Testing tools
  2. Write own code to test

Why should we do API Testing?

API testing exposes any bugs or errors in API and resolves them at early stages. It checks an application's core functionality and evaluates the build’s strength. The primary concerns of API testing are:

  • To narrow down probabilities of applications crashes or bugs later.
  • Security concerns of the API
  • It makes GUI testing easier.
  • Allows components of software to be deployed quickly.
  • Enables faster releases.

How to Perform API Testing? 

Generally, all the applications have three layers:

  1. Presentation layer
  2. Business layer
  3. Database layer 

The API testing concentrates on the business layer. All the data fetching and exchange between the user and database is done in the business layer. 

Source

The process of API testing is listed below:

The first step is to create a document of API testing requirements. It contains the purpose of API, the application's workflow and integrations, features supported by the API. The API specifications and use cases documentation is reviewed from the test perspective.

1. Test environment setup:

The testing environment is developed with the required set of parameters necessary for the API. The database and the servers are configured for the application requirements.

2. Application data integration:

We must integrate the API tests with the application to ensure the API functionality is similar to what we expected against all possible scenarios or input configurations.

3. API test specification:

After creating the testing boundaries and requirements, we need to decide what tests to run on the API. There are different types of API tests, which we will discuss further in this article.

4. Test execution and reporting:

Test case development is done by coding test scenarios, creating sanity check test suites around the requirements. After the development is done, we execute the tests with possible parameters and conditions a user might call. Then we report the complete test scenario and result.

Types of API Testing

1. Functional Testing:

 Functionality tests make sure that all the APIs are working and doing what exactly they are supposed to do.

2. Reliability Testing: 

Reliability testing makes sure that the API works in case of connecting it to various devices gives consistent results.

3. Load Testing: 

Load tests check whether the API responds to all the servers it gets a request from under any circumstances.

4. Stress Testing: 

Stress testing checks whether the API works as intended when the API receives several requests.

5. Security Testing: 

Security tests check whether the API is secure against all possible threats and breaches. It ensures no security breaches happen and no unnecessary data is shared while giving an authentication, 

6. Integration Testing: 

Integration tests check whether all the APIs are connected and if bugs in any API causes bugs in APIs dependent on it.

7. UI Testing:

UI testing involves testing the user interface for the API, other integral parts, and whether the user experience is smooth using them.

8. Penetration Testing:

Penetration testing detects vulnerabilities of an application from an attacker's perspective.

9. Validation Testing:

Validation test verifies the aspects of an API's product, behavior, and efficiency.

List of Popular API Testing Tools

We need to use a tool to perform successful testing and manage them. Here’s a list of tools we can use to perform our test:

  1. SoapUI
  2. Postman
  3. Katalon studio
  4. Tricentis Tosca
  5. REST-assured
  6. Apigee
  7. Karate DSL

Challenges of API Testing

  • A GUI is a must for testing because the tester might face difficulties giving inputs without it.
  • The main challenges are parameter selection, parameter combination, and call sequencing.
  • Test case management is complex since a tester has to manage millions of cases.
  • Exceptions should be reproduced every time to test exception handling functions.
  • Improper documentation might provide ambiguous information about API working.
  • Time-consuming and needs a lot of resources.
     

Related Article Sanity Testing vs Smoke Testing

FAQs

  1. What is API testing?
    API testing is software testing, where an API is tested to check whether it exhibits expected functionality, performance, reliability, and security. 
     
  2. What is an API?
    API (Application Programming Interface) is an intermediate software that helps communication between UI and backend. It is a set of functions that allow the creation of applications that access data and other features of other applications, services, or operating systems.
     
  3. What is the best tool for API testing?
    There any many tools available to test an API. The most used among them are SoapUI, Postman, Apigee, etc.

Key Takeaways

Let's sum up this article to get a brief knowledge on API testing:

  • API - Application Programming Interface is an intermediate software that helps communication between UI and backend. They define the rules that programmers/developers must follow to interact with a programming language, a software library, or any software. 
  • API testing is software type testing, where an API is tested to check whether it exhibits expected functionality, performance, reliability, and security. 
  • API testing exposes any bugs or errors in API and resolves them at early stages. It checks an application's core functionality and evaluates the build’s strength.
  • The testing of API is done on the business layer because it contains the Application User interface.
     

Hello Ninjas! Aren’t APIs fun to work with? Enroll in the best web development course to learn more about APIs and their testing.
 
Happy Learning!

Live masterclass