Testing starts from the requirements phase only when the 
developer is collecting bussiness requirments we testers 
should collect the test requirments 
1.Functional requirement Document 
2.Non Functional requirement Document 

Hi 
Testing starts when the SRS are ready.
Tester starts writing test cases where as developer starts 
coding for the requirements of a particular module

testing starts as soon as the requirements are freezed.
as soon as the SRS is finished, the srs comes to the 
testing department.
the test engineers go through the srs document.if they get 
the doubts they will clarify from the author of the srs.
after that they will understand all the requirements
and they will take the test case template and starts 
writting the test cases and tehy will execute them

As confirmed by everyone, testing should start at 
requirement gathering stage. 

The cost of finding a defect at a later stage would be more 
costlier rather finding it at the first stage itself.

Gap analysis is done at this stage.[gap analysis - is used 
to find out the gaps in the system\documents with the 
baselined SRS).