What is API testing and What are its types?

What is API testing?

API Testing is known as Application Programming Interface, which enables communication and data exchange between two different systems. It defines the protocols of how two systems will interact/communicate with each other. It is a type of software testing which validates APIs. The applications have three layers:

  • Presentation Layer(User Interface)
  • Business Layer(Application User Interface)
  • Database Layer(Database)

The API works on the Business layer, and it defines the rules of how a user will interact with the data, services or the functions of the app. In the software development, the API layer is the middle layer which lies between the presentation layer and database layer. It is entirely different from GUI Testing.

This testing is performed to check the reliability, security, functionality and performance of the programming interfaces. The API testing will not focus on the look and feel of the application. It concentrates on the business logic of the software architecture.

API Testing

How does the API works?

Now when you have studied the API testing, you have a question in mind. How does this API work? What will be the logic behind this? Do we use this technique in the real world?

Today we will discuss some real-world examples. With these examples, you will get an answer to your questions.

Have you tried to book flights online?

When you try to book a flight, then you enter the flight details in the search bar. For example, you want to travel from Delhi to Banglore.

When you enter these details, then you will get the price list from different airlines. When you enter the details, then the application sends an API request to various airlines. The API takes the airlines response and get back to you with the requested data. So this is how an API works.

Have you tried to book hotels online?

In today’s world, everyone is aware of Trivago. Many of you must have used this application. But do you know about the working of this application? How it delivers you the data from different hotels?

This process also works on APIs. Whenever you search for hotels around you, then it sends API requests to different hotels and then gets the data from there. Then it shows you the matching results.

In today’s world, we use this daily in our daily life. If still, you have some doubts regarding this, then do let us know in comments.

Benefits of API Testing

  • Earlier testing can be performed.
  • It requires less code so you will get better and faster test coverage.
  • It is language Independent.
  • API testing reduces the cost of testing.
  • It also reduces risks.
  • Test Maintenance is easy.

Types of API Testing

  • Functional Testing
  • Validation Testing
  • Unit Testing
  • Load Testing
  • UI Testing
  • Security TEsting
  • Penetration Testing
  • Fuzz Testing
  • Run time error detection
  • WS Compliance Testing

Different Testing Tools

  • Runscope
  • Curl
  • Postman
  • Fix
  • Check
  • SoapUI
  • Jmeter
  • Katalon Studio
  • vREST
  • Parasoft
  • HttpMaster
  • LoadFocus
  • PingAPI
  • Airborne

What type of bugs can be detected by this type of testing?

  • Functionality Bugs
  • Performance Bugs
  • Reliability Bugs
  • Security Bugs
  • Multi-threading Issues are also detected.
  • Data related defects are also detected by API Testing.
  • Improper errors
  • Improper errors to the caller
  • Sometimes the response data is not structured correctly (JSON/XML) can also be detected by performing this testing.

What are the differences between Unit Testing and API Testing?

Unit TestingAPI Testing
Developers perform this testingTesters perform this testing.
It is a type of White Box Testing.It is a type of Black Box Testing.
You can test separate functionality in Unit Testing.You can test end to end functionality.
The developers can access the source code.The testers cannot access the source code.
It is limited in scope.It is broader in scope.
In unit testing, UI testing is also involvedIn this testing, We can test only the API functions.
Unit Testing is performed before the CheckinIt can be performed after built is created.

Challenges in API testing:

  • The main challenge that we face is with the parameter combination. So we need to select the proper parameter and proper combination.
  • As there is no GUI available that also makes it difficult to input values.
  • Another main challenge that we face is with call sequencing.
  • Verifying and validating outputs is also a little bit difficult.
  • The tester should have the coding language.
  • It would be best if you categorized the parameters correctly.

Best practices for API Testing

  • You need to test for the expected results first.
  • It would be best if you grouped the test cases by test category.
  • Add stress to the system, and a series of API load tests can do it.
  • It would be best if you prioritized API functions so that it will become more comfortable for the tester to test them quickly.
  • Special care must be provided when you handle one-time call functions like Delete, close window etc.
  • You need to perform a well-planned call sequencing.
  • Create test cases for all possible API inputs for the complete test coverage.
  • Whenever it is possible, you can automate API testing.

In this post, we have discussed regarding what is API testing, what are its types, what are the benefits etc. In the upcoming post, we will discuss the top 15 questions that can be asked based on API testing. If you want to read or just started the software testing course, then you can click here to read about Software testing.