Testing methodology is a sore subject for most pentesters. Everyone has their own way to do things, and 3 people testing the same thing often end up with different results—especially when constrained for time.
The ASTM project has two goals: 1) allow testers to consistently find the best vulnerabilities in the shortest amount of time, and 2) provide a framework for community improvement of the methodologies.
ASTM combines a time restraint with a quick technology detection step to build a customized testing methodology for that specific website given how much time you have to test it.