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.
