You need Python 2.6 or higher. Then clone this repo:
git clone git://github.com/mozilla/test-amo-validator.git
Install the dependencies:
cd test-amo-validator pip install -r requirements.txt
In addition to this command you also need to build spidermonkey from source as detailed in amo-validator's install instructions.
cd test-amo-validator nosetests --processes=2
Then make a cup of tea while all of those tests run. It takes a while. If you have more than two cores on your machine or you don't mind pwnage, you can try to increase the number of parallel processes used for testing.