API is an acronym for Application Programming Interface. An API is a set of procedures, methods, and functions that developers “open up” to other programmers in order to have their applications interact and communicate with other applications. Once an API is built, it is necessary to test the interface to make sure it is working properly.

API testing is different from UI testing, and it mainly concentrates on the use of software to send API calls, receiving outputs, and logging the system responses. API test investigates applications that have varying API functionalities and varies the parameters of the API calls in different ways that verify functionality and expose failures.

Here is a diagram of where API testing typically comes into play:

API Test code: What should be performed –

The API test code or test “harness” should send different parameter combinations through the API, and the return values based on input conditions should be checked. API testing is the only way to provide truly secure, reliable, and scalable connections between platforms.

API Testing Benefits :

1. Access to the application without user interface

The major core advantage of API testing is that it provides access to applications without users actually having to interact with a potentially disparate system. This helps the tester to detect and recognize the errors early, instead of them becoming larger issues during GUI testing.

2. Protection from malicious code and breakage

API test requires extraordinary conditions and inputs, which protect the application from malicious code and breakage. Basically, API tests push software to their connective limits. API testing helps remove vulnerabilities.

3. Time Efficiency vs. functional and validation testing

API testing is far less time-consuming than functional and validation testing. 10,000 automated API tests save 3 hours of time on average vs. functional and validation testing.

4. Cost Effective / Reduces Testing Cost

API test automation requires less code than GUI automated tests thus providing faster test results and better test coverage. The end result of faster testing is a reduction in overall testing costs. Testing the API level functionality of the application provides an early evaluation of its overall build strength before running GUI tests. Early detection of errors reduces the manual testing cost. API test automation increases the depth and scope of the tests.

5. Technology Independent

In an API test, the data is interchanged using XML or JSON and compromised of HTTP requests and responses. These all are technology independent and used for development. Thus an API test allows you to select any core language when using automated API testing services for your application.

API Testing Tools:

There are many API testing tools available such as:

1. JMeter

JMeter is an open-source API testing tool available on the market for API testing. JMeter provides easy integration with Jenkins to run the test periodically and Jenkins has a plugin for Jmeter to parse the result file and display the charts.

2. Eclipse IDE Java SDK tool – Automated API testing tools

Eclipse IDE Java SDK is an open-source API testing tool, which helps in consuming RESTful web services with Jersey Client API. Jersey client API is an easy-to-use, high-level, Java technology API that can help you write clients for any HTTP-based RESTful web service.

3. Test Manager

Test Manager is a tool to test API by sending requests like GET() and POST() and receiving a response from a particular application server or web server. The user enters the specific IP address, port address and then creates a new request with input parameters. On successful execution of a script, a response is received like ‘200 OK’. Some more tools like Hurl, Fiddler, Runscope, dotTest are also available for API testing.