API stands for Application Programming Interface, which describes how one component will interact with the other. It contains a set of routines, protocols, and tools to make the software applications.
Routine: It’s a program that performs a specific task. Routine is also called as procedure, function, or subroutine.
Protocols: It’s a format to transmit data between the two systems.
If we are using a flight service engine, where we search for flights on a particular date. Once we enter the data such as Source, Destination, Onward Date, and Return Date, and click on search. Expedia sends a request to airlines through an API as per the search details. The API then takes the airline’s response to our request and delivers it right back to Expedia.
API receives the request from the user and gives the response without exposing internal logic.
What is API Testing?
API testing involves the testing of APIs directly to check whether the API meets the requirements in terms of functionality, reliability, performance, and security of an application. Our main focus should be on a Business logic layer of the software architecture in API Testing. It can be performed on any software system having multiple APIs.
The API Testing is performed for the system, which contains a collection of API that need to be tested. A test of the following things need to be considered while testing:
- Exploring boundary conditions to ensure that the test harness varies parameters of an API calls in ways that verify functionality and expose failures.
- Generating more value added parameter combinations to check the calls with two or more than two parameters.
- Verifying the behavior of an API with the external environment conditions like files, peripheral devices, etc.
- Verifying the Sequence of an API call and checking if the API’s produce useful results from successive calls.
API Testing Types?
There are the following types of API testing
- Unit testing: A testing technique to test the functionality of individual modules
- Functional testing: A technique to test the functionality of the system software and it should cover all the scenarios by using a block of unit test results tested together
- Load testing: To test the functionality and performance under real life based load conditions.
- Runtime/Error Detection: To monitor an application to analyze the problems such as exceptions and resource leaks as it executes and reports the defects that were found during that execution.
- Security testing: To ensure that the implementation of the API is secure from external threats, vulnerabilities, threats, risks in a software application to prevent malicious attacks
- UI testing: It is performed as part of end-to-end integration tests to validate the expected performance and functionality and make sure that every aspect of the user interface functions is working as expected
- Interoperability and WS Compliance testing: The type of software testing ensures that Interoperability and WS Compliance testing applies to SOAP APIs. Interoperability testing between SOAP APIs is verified by conformance testing to the Web Services Interoperability profiles. WS-*
- Penetration testing: It is a practice of testing to find security vulnerabilities of an application from attackers
- Fuzz testing: It’s a testing technique to test the API by forcibly or unexpected input into the system in order to attempt a forced crash
Common Tests performed on API’s
- Return Value of an API is based on the input condition
- Verify if API doesn’t return anything.
- Verify if the API triggers some calls or an event from another API. The output of an event should be tracked and verified.
- Validate if the API is updating any data structure.
Advantages of API Testing:
- API Testing becomes time effective when it gets compared to GUI Testing. API test automation provides faster and better test coverage because it requires less code
- Testing costs can be reduced with API Testing. With API Testing, we can find minor bugs before the GUI Testing because these minor bugs may become larger during GUI Testing. So getting those bugs in the API Testing can be cost-effective for the company.
- API Testing is language independent.
- For testing Core Functionality, API Testing is quite helpful. APIs can be tested without a user interface. For GUI Testing, we have to wait until the application gets available to test the core functionalities.
- API Testing helps us to reduce the risks.
What should be verified in API Testing?
In the API Testing, we send a request to the API with the known data and on the basis of that data we analyze the response for:
- Data accuracy
- HTTP status codes
- Response time
- Error codes (In case API return any errors)
- Authorization checks
- Non-functional testing like (Performance testing, Security testing)
Tools used for API Testing:
There are many tools for API Testing and a few of them are as follows:
- API Fortress
- HP QTP(UFT)
- API Science
- HttpMaster Express
- Ping API
- Rest Console
- SOAP Sonar
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