How to run a single RSpec test?

With Rake:

rake spec SPEC=path/to/spec.rb

(Credit goes to this answer. Go vote him up.)

EDIT (thanks to @cirosantilli): To run one specific scenario within the spec, you have to supply a regex pattern match that matches the description.

rake spec SPEC=path/to/spec.rb \
          SPEC_OPTS="-e \"should be successful and return 3 items\""

Usually I do:

rspec ./spec/controllers/groups_controller_spec.rb:42

Where 42 represents the line of the test I want to run.

You can also use tags. See here.

Using bundle exec:

bundle exec rspec ./spec/controllers/groups_controller_spec.rb:42