VERSION INFO: tox 1.6.1 with python 2.7, virtualenv 0.10.1, setuptools 0.9.8 (or newer)
When you use the new "install_command" with easy_install you get an error when you run the same test environment twice without recreating it. The problem occurs in the sdist installation step because 2 options "-U --no-deps" are appended after the package.
shell> tox -e xxx -r
shell> tox -e xxx
error: Could not find suitable distribution for Requirement.parse('-U')
The problem is the last 2 options "-U --no-deps" that are appended to the easy_install command-line. When you place these 2 options before the package, easy_install is happy and will install the package at the second time.