Run single system test

To run a single test in Rails, we normally do:

rails test TEST=test/system/invitation_test.rb

But that doesn't work with system tests. Neither do this work:

rails test:system TEST=test/system/invitation_test.rb

With both those commandos above, all system tests (files) are run.

As a side note, to run all system tests in Rails, you'd do:

rails test:system