How do I run Rake tasks within a Ruby script?

from timocracy.com:

require 'rake'

def capture_stdout
  s = StringIO.new
  oldstdout = $stdout
  $stdout = s
  yield
  s.string
ensure
  $stdout = oldstdout
end

Rake.application.rake_require 'metric_fetcher', ['../../lib/tasks']
results = capture_stdout {Rake.application['metric_fetcher'].invoke}