After running a group of tests -- whether it is the entire suite or just the
tests in a file -- you may find that you have a few failures. Often the goal is
to focus in on these failures and get back to a green test suite. Rather than
rerunning everything each time you make a change, you can instruct rspec to
just rerun the tests that failed. This can be done with the --only-failures
flag or --on flag for short.