Pre Synthesis means - The process which is done before doing the synthesis.
Post Synthesis : The process which is done after synthesis..
mostly pre and post means that before and after respectively.
STA : is just static timing analysis means, it will not apply any patterns to design, but just doing the timing analysis for 0->1 and 1->0 transitions on net and logic.
While DTA : is just simulation with patterns. So we can check that, Timing analysis which is done by STA is working fine or not..
I don't think that there is any difference between testing and validation.
Thanks
Maulin