RSpec was chosen to be used for acceptance tests for many reasons:
* The tests are actually much cleaner now. It is clearer to see what
is being tested, and what is being used for setup.
* Matcher transition will be coming soon. This will really clean up
a lot of the "assert" boilerplate all over. There was a lot of repetition
in this area.
* Shared examples will help greatly for testing common error cases
for many commands.
* The test runner for RSpec is simply much better. Being able to specify
the exact test to run by line, for example, is a great help.
Mitchell Hashimoto