Answer / anant

Before dwelling into the subject of API Testing, we should
understand what is the meaning of API or, Application
Programming Interface.

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. It is very easy to setup initial condition in
GUI, In most cases you can find out in a glance whether
system is ready or not. In case of API this is not the
case, you need to have some way to make sure that system is
ready for testing.

This can be divided further in test environment setup and
application setup. Things like database should be
configured, server should be started are related to test
environment setup. On the other hand object should be
created before calling non static member of the class falls
under application specific setup.

Initial condition in API testing also involves creating
conditions under which API will be called. Probably, API
can be called directly

or it can be called because of some event or in response of
some exception.

Output of API could be some data or status or it can just
wait for some other call to complete in a-synchronized
environment. Most of the test cases of API will be based on
the output, if API

Return value based on input condition

This are relatively simple to test as input can be defined
and results can be validated against expected return value.
For 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

For cases like these you will probably have some mechanism
to check behavior of API on the system. For example, if you
need to write test cases for delete(ListElement) function
you will probably validate size of the list, absence of
list element in the list.

Trigger some other API/event/interrupt

If API is triggering some event or raising some interrupt,
then you need to listen for those events and interrupt
listener. Your test suite should call appropriate API and
asserts 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. If
you have other means of accessing the data structure, it
should be used to validate that data structure is updated.

Modify certain resources

If API call is modifying some resources, for example
updating some database, changing registry, killing some
process etc, then it should be validated by accessing those
resources.

You should not get confused with API Testing and Unit
Testing. API testing is not Unit testing. Unit testing is
owned by dev team and API by QE team. API is mostly black
box testing where as unit testing is essentially white box
testing. Unit test cases are typically designed by the
developers and there scope is limited to the unit under
test. In API testing, test cases are designed by the QE
team and there scope is not limited to any specific unit,
but it normally cover complete system.

Main Challenges of API Testing can be divided into
following categories.

Parameter Selection
Parameter combination
Call sequencing

Answer / abdul sameer

A formalized set of software calls and routines that can be
referenced by an application program in order to access
supporting system or network services.

i have faced this question in one interview.kindly let me know if u know the ans . the ques is the tester have been found 20 bugs in the requirement .after dev. has been fixed 20 bugs again tester retest the bugs he found again 12 bugs dev .fixed 12 bugs keep on its going ..finally its comes zero defects now how will u checking the application stability ..

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