I will use Adhoc Testing.

Adhoc Testing: Testing the product without knowing the 
functional requirments but knowing the internals of the 
application.

at this time we use to conduct adhoc testing
involved people are highly skilled persons

Then we go for adhoc testing which is based on pre defined 
ideas of test engineer from his past experiance

it is impossible to test the appls without the F.S.
testing intension is to verify whether the developed appl 
is according to the customer requirement or not.
but we can do exploratory and adhoc testing.
they don't require any testcases or doc's/
with the knowledge on the domain we can do.
in real time no timelines are there for these tests.

Dear All,

I am appreaciate ur answers but try to give correct answers

Adhoc means it is process less testing 
But in this position we should be go for EXPLORATORY 
testing.Means by explorating application we learn the 
functionality as well as test the functionality