requirements phase it self

test plan prepares in each and every phage in In vlidation 
phase that is right hand side

designing phase

The test plan will be prepared in various stages in a V 
Model.

The UAT Test plan will be prepared at the requirement 
analysis phase as one of our friend has said and the System 
test plan will be prepared during the High Level Design 
Phase. The integration test plan during the Low Level 
Design phase.

a rough test plan at requirements phase
testplan at hld phase
according to that every activity will be done.
like templates used inside
inscope and outscope
milestones
terminology
risks and mitigation plans
and so on.
so plan is there from the beginning.

1> System test plan in requirement analysis phase;
2> Integration test plan in High level Design phase;
3> Module test plan in Low Level Design phase;