which test should we do first?

We can’t test every thing. There is never enough time to do all testing you would like, so what testing should you do?

Prioritize Tests. So that, whenever you stop testing, you have done the best testing in the time available.

Tips

Possible ranking criteria ( all risk based)

Test where a failure would be most serve.

Test where failures would be most visible.

Take the help of customer in understanding what is most important to him.

What is most critical to the customers business.

Areas changed most often.

Areas with most problems in the past.

Most complex areas, or technically critical.