API Testing

API Testing

An API (Application Programming Interface) is a collection of software functions and procedures, called API calls that can be executed by other software applications.

API testing is mostly used for the system which has collection of API that needs to be tested. The system could be system software, application software or libraries. API testing is different from other testing types as GUI is rarely involved in API Testing. Even if GUI is not involved in API testing, you still need to setup initial environment, invoke API with required set of parameters and then finally analyze the result. Setting initial environment become complex because GUI is not involved. In case of API, you need to have some way to make sure that system is ready for testing.

Test Cases for API Testing:

The test cases on API testing are based on the output.

•Return value based on input condition

Relatively simple to test as input can be defined and results can be validated. Example: It is very easy to write test cases for int add( int a, int b) kind of API. You can pass different combinations of int a and int b and can validate these against known results.

•Does not return anything

 Behavior of API on the system to be checked when there is no return value.

Example: A test case to delete (List Element) function will probably require validating size of the list or absence of list element in the list.

•Trigger some other API/event/interrupt

 The output of an API if triggers some event or raises some interrupt, then those events and interrupt listeners should be tracked. The test suite should call appropriate API and declarations should be on the interrupts and listener.

•Update data structure

This category is also similar to the API category which does not return anything. Updating data structure will have some effect on the system and that should be validated.

•Modify certain resources

 If API call is modifies some resources, for example makes update on some database, changes registry, kills some processes etc., then it should be validated by accessing the respective resources.

API Testing Approach

An approach to test the Product that contains an API.

Step I: Understand that API Testing is a testing activity that requires some coding and is usually beyond the scope of what developers are expected to do. Testing team should own this activity.

Step II: Traditional testing techniques such as equivalence classes and boundary analysis are also applicable to API Testing, so even if you are not too comfortable with coding, you can still design good API tests.

Step III: It is almost impossible to test all possible scenarios that are possible to use with your API. Hence, focus on the most likely scenarios, and also apply techniques like Soap Opera Testing and Forced Error Testing using different data types and size to maximize the test coverage. Main Challenges of API Testing can be divided into following categories.

In Automation API Testing shows in the following picture.