This isn't working. Or something isn't working, anyhow.

Guardfile

# More info at https://github.com/guard/guard#readme

guard 'minitest' do
  # with Minitest::Unit
  watch(%r{^lib/(.+)\.rb$})     { |m| "test/#{m[1]}_test.rb" }
  watch(%r{^test/.+_test\.rb$})
  watch('test/test_helper.rb')  { "test" }

  # Rails example
  watch(%r{^app/models/(.+)\.rb$})                   { |m| "test/unit/#{m[1]}_test.rb" }
  watch(%r{^app/controllers/(.+)\.rb$})              { |m| "test/functional/#{m[1]}_test.rb" }
  watch(%r{^app/views/.+\.rb$})                      { "test/integration" }
  watch('app/controllers/application_controller.rb') { ["test/functional", "test/integration"] }

  # with Minitest::Spec
  # watch('^spec/(.*)_spec.rb')
  # watch('^lib/(.*)\.rb')                            { |m| "spec/#{m[1]}_spec.rb" }
  # watch('^spec/spec_helper.rb')                     { "spec" }
end