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Rajat Thakur
Rajat Thakur

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What is API Test Automation?

What is API?

API (Application Programming Interface) is a processing interface that enables communication and data exchange between two separate software systems. A software system running an API includes several functions/routines that another software system can perform.

The API defines the queries that can be made, such as queries, usable data formats, etc. between two software systems. Our team has created a news API and we also used these points and many tools for testing that.

What is API testing?

TEST API is a type of software test that validates application programming interfaces (APIs). The objective of API testing is to verify the functionality, reliability, performance, and security of programming interfaces.

In API tests, instead of using standard user input and output (keyboard), you use software to send API calls, get output, and note the system response. API testing is very different from GUI testing and will not focus on the appearance of an application. It mainly focuses on the business logic layer of software architecture.

API automation Testing requires an application that can be interacted via an API. In order to test an API, you will need to

  • Use Testing Tool to drive the API
  • Write your own code to test the API

Set-up of API Test environment

  • The test API differs from other types of software testing in that the GUI is not available, but an initial environment must be configured to call the API with a set of required parameters and then examine the test result.
  • So setting up a test environment for API automation testing seems a bit complex.
  • The database and the server must be configured according to the requirements of the application.
  • Once the installation is complete, the API function should be called to check if this API is working.

Types of Output of an API

An output of API could be

  • Any type of data
  • Status (say Pass or Fail)
  • Call another API function.

Status (say Pass or Fail)

Consider the below API function –

  • Lock()
  • Unlock()
  • Delete()

They return any value such as True (in case of success) or false (In case of error) as an output.

A more accurate Test Case would be, can call the functions in any of the scripts and later check for changes either in the database or the Application GUI.

Calling of another API / Event

In this case, we call one of the API functions which in turn will call another function.

For example — The first API function can be used for deleting a specified record in the table and this function, in turn, calls another function to REFRESH the database.

Test Cases for API Testing:

Test cases of API testing are based on

  • Return value based on input condition: It is relatively easy to test because the input can be set and the results can be authenticated
  • Returns nothing: when there is no return value, API behavior on the system to be verified
  • Activate another API / event/interrupt: if an output of an API triggers an event or an interrupt, these events and interrupt listeners must be tracked
  • Update the data structure: updating the data structure will have a result of an effect on the system, and it must be authenticated
  • Modify some resources: if an API call modifies some resources, then it must be validated in accessing the respective resources.

API Testing Approach

The API testing approach is a predefined strategy or method that the QA team will execute to perform API testing after the build is ready. This test does not include source code. The API test approach helps you better understand functionality, technical testing, input parameters, and test case execution.

The following steps help you perform the API testing approach:

  • Understand the functionality of the API program and clearly define the scope of the program
  • Apply testing techniques such as equivalence classes, analysis of limit values ​​and error assumptions, and write test cases for API
  • Input parameters for API must be properly planned and set
  • Run test cases and compare expected results to results real.

Difference between API testing and Unit testing

Image description

How to Test API

API automation tests should cover at least the following test methods in addition to the usual SDLC process.

  • Discovery test: The test group should manually run all of the calls documented in the API, for example, to verify that a specific resource exposed by the API can be listed, created, and deleted as needed.
  • Usability test: This test checks if the API is functional and easy to use. And does the API also integrate well with another platform?
  • Security test: This test includes the type of authentication required and whether sensitive data is encrypted over HTTP or both.
  • Automated Tests: API tests should result in the creation of a set of scripts or a tool that can be used to run the API on a regular basis.
  • Documentation: The test team should ensure that the documentation is adequate and provides enough information to interact with the API. Documentation should be part of the end result.

Best Practices of API Testing:

  • API test cases should be grouped by test category.
  • At the top of each test, you must include the declarations of the called API.
  • The selection of parameters must be explicitly mentioned in the test case itself.
  • Prioritize API function calls so that it is easy for testers to test.
  • Each test case should be as self-contained and independent of dependencies as possible.
  • Avoid “test chaining” in your development.
  • Special care should be taken when dealing with occasional call functions such as — Delete, Close window, etc.
  • The call sequence should be executed and well planned.
  • To ensure complete test coverage, create API test cases for all possible combinations of API inputs.

Types of Bugs that API testing detects

  • Cannot properly handle error conditions
  • Unused flags
  • Missing or duplicate functionality
  • Reliability issues. Difficulty logging in and getting a response from the API.
  • Security issues
  • Multithreading issues
  • Performance issues The API response time is very high.
  • Incorrect errors/warnings to a caller
  • Incorrect handling of valid argument values ​​
  • The response data is not structured correctly (JSON or XML)

Challenges of API Testing

API testing challenges include:

  • The main challenges of web API testing are a combination of parameters, parameter selection, and call sequence
  • There is no GUI available to test the application, which makes it difficult to provide values ​​
  • Validating and verifying the output in a different system is a bit difficult for testers
  • Parameter selection and categorization must be known to testers
  • Exception handling function must be tested
  • For testers, it is necessary to know the coding


The API consists of a set of classes/functions/procedures that represent the business logic layer. If the API is not tested correctly, it can cause problems not only for the API application but also for the calling application. It is an essential test in software engineering.

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