Normally you run tests through rake tasks from the command line: rake (to test everything), rake test:functionals (to test all controllers) or rake test:units (to test all models). Sometimes it is useful to run single tests for a particular model..
> ruby test/unit/group_test.rb
..or for a special controller..
> ruby test/functional/groups_controller_test.rb
from the command line. See also here
4 Lines of Code 