What is the point of setting TESTOPTS="-v" with `rake test`?

I'm using rake/testtask in my app to generate the conventional :test task.

The examples demonstrate adding TESTOPTS="-v" to the command to turn on "verbose" mode:

rake test TESTOPTS="-v"             # run in verbose mode

(http://ift.tt/1L2DICR)

Now, I've looked at the source code for rake/testtask, as well as wrote some code to test behaviour. It's passing that env var on to the shell process it invokes to run the test file (via ruby command), and I can see the value set inside my test file.

However, what is it for? Who is intended to receive/use it?

I'm currently using minitest, and it doesn't affect behaviour. In fact, I searched the minitest repo for any instance of "testopts" and found nothing:

http://ift.tt/1VzF5mL

So, is this a Test::Unit or RSpec feature? Is no one currently hooking into this option? Why isn't any of this explained in the docs?