If you look at the bin directory in your virtualenv, you’ll see easy_install which has been modified to put eggs and packages in the virtualenv’s site-packages directory. To install an app in your virtual environment:

$ source test_project/bin/activate
$ pip install flask

At this time, you don’t have to use sudo since the files will all be installed in the local virtualenv site-packages directory. This was created as your own user account.