API Testing Tutorial: What is API Test Automation? How to Test

What is API?

API (Application Programming Interface) is a computing interface which enables communication and data exchange between two separate software systems. Software system that executes an API includes several functions/subroutines that another software system can perform. API defines requests that can be made, how to make requests, data formats that can be used, etc. between two software systems.

What is API Testing?

API TESTING is a software testing type that validates Application Programming Interfaces (APIs). The purpose of API Testing is to check the functionality, reliability, performance, and security of the programming interfaces. In API Testing, instead of using standard user inputs(keyboard) and outputs, you use software to send calls to the API, get output, and note down the system’s response. API tests are very different from GUI Tests and won’t concentrate on the look and feel of an application. It mainly concentrates on the business logic layer of the software architecture.

Set-up of API Test environment

• API Testing is different than other software testing types as GUI is not available, and yet you are required to setup initial environment that invokes API with a required set of parameters and then finally examines the test result.
• Hence, Setting up a testing environment for API automation testing seems a little complex.
• Database and server should be configured as per the application requirements.
• Once the installation is done, the API Function should be called to check whether that API is working.

Test Cases for API Testing

• Return value based on input condition: it is relatively easy to test, as input can be defined and results can be authenticated
• Does not return anything: When there is no return value, a behavior of API on the system to be checked
• Trigger some other API/event/interrupt: If an output of an API triggers some event or interrupt, then those events and interrupt listeners should be tracked
• Update data structure: Updating data structure will have some outcome or effect on the system, and that should be authenticated
• Modify certain resources: If API call modifies some resources then it should be validated by accessing respective resources

API Testing Approach

API Testing Approach is a predefined strategy or a method that the QA team will perform in order to conduct the API testing after the build is ready. This testing does not include the source code. The API testing approach helps to better understand the functionalities, testing techniques, input parameters and the execution of test cases.

Following points helps the user to do API Testing approach:

1. Understanding the functionality of the API program and clearly define the scope of the program
2. Apply testing techniques such as equivalence classes, boundary value analysis, and error guessing and write test cases for the API
3. Input Parameters for the API need to be planned and defined appropriately
4. Execute the test cases and compare expected and actual results.

How to Test API

API testing is a crucial aspect of software development as it helps ensure the functionality and performance of APIs. There are several types of API testing, including unit testing, functional testing, load testing, security testing, and penetration testing.

1. Unit Testing: This type of testing involves testing individual API methods or functions. It helps ensure that each method performs as intended and returns the correct output.
2. Functional Testing: This type of testing involves testing the overall functionality of the API. It checks whether the API works as intended, including verifying that inputs are processed correctly and outputs are generated properly.
3. Load Testing: This type of testing involves testing the API’s ability to handle a large number of requests simultaneously. It helps identify the API’s performance under heavy load and ensures that it can handle traffic without crashing or slowing down.
4. Security Testing: This type of testing involves testing the API’s security features to ensure that it is protected against unauthorized access, data theft, and other security vulnerabilities.
5. Penetration Testing: This type of testing involves simulating an attack on the API to identify vulnerabilities that can be exploited by hackers. It helps ensure that the API is secure and protected against potential attacks.

It is essential to conduct API testing regularly to identify and resolve any issues before they affect the end-user experience. By leveraging these different types of API testing, developers can ensure that their APIs are reliable, performant, and secure.

Best Practices of API Testing

• API Test cases should be grouped by test category
• On top of each test, you should include the declarations of the APIs being called.
• Parameters selection should be explicitly mentioned in the test case itself
• Prioritize API function calls so that it will be easy for testers to test
• Each test case should be as self-contained and independent from dependencies as possible
• Avoid “test chaining” in your development
• Special care must be taken while handling one-time call functions like – Delete, CloseWindow, etc…
• Call sequencing should be performed and well planned
• To ensure complete test coverage, create API test cases for all possible input combinations of the API.

Types of Bugs that API testing detects

• Fails to handle error conditions gracefully
• Unused flags
• Missing or duplicate functionality
• Reliability Issues. Difficulty in connecting and getting a response from API.
• Security Issues
• Multi-threading issues
• Performance Issues. API response time is very high.
• Improper errors/warning to a caller
• Incorrect handling of valid argument values
• Response Data is not structured correctly (JSON or XML)

Challenges of API Testing

• Main challenges in Web API testing is Parameter Combination, Parameter Selection, and Call Sequencing
• There is no GUI available to test the application which makes difficult to give input values
• Validating and Verifying the output in a different system is little difficult for testers
• Parameters selection and categorization is required to be known to the testers
• Exception handling function needs to be tested
• Coding knowledge is necessary for testers