completion of intgration testing is the entry criteria for 
system testing
when to stop testing defficult to decide,some common 
factors on deciding are
1.testcases completed with certain % of pass
2.Releasing and testing deadlines 
3.test budget depleted
4.coverage of requirements
5.beta and alpha testing period ends

 hi this is satya ,any doubts contact:991212418320

hi Satya prakash, sateesh is not asked when system testing 
starts..when testing is start and stop...

In every project , testing starts with Requirements 
capture.. in Requirements stage static testing is 
going ..after coding ..there is so many testin grelated to 
functionality and so many thingss...

If i am wrong please correct me...

hi surendra here u have explained only when testing was
started right.
This is for new application: Actually first half all we are
receiving requirements from client we are starting the
testing depending upon the requirements we have to prepare
test cases we are sending the client he also check ones (it
contains only expected values)
After that we are doing testing for each phase from SDLC
After completing the testing phase and fixed all bugs in
that time only we have to stop.
Stop conditions:1)Project deadlines will come
2)project is completed with bug free product.
If already developed application means:
We have to perform “Sanity Testing” after that we are doing
other tests depending upon requirements.

Acutally this is a difficult question to be answered. Since 
Testing is a continous process as one can't assure any 
product 100% bug free in this world. Anyhow, the 
considerations are: 

a) Deadlines. 
b) Coverage of requirements / specifications. 
c) Test Cases completed with certain percentage passed. 
d) When Bug rate falls below a certain level.  
e) Test Budget depleted.