Guardfile

guard :minitest do
 # with Minitest::Unit
 watch(%r{^test/(.*)\/?test_(.*)\.rb$})
 watch(%r{^lib/(.*/)?([^/]+)\.rb$}) { |m| "test/#{m[1]}test_#{m[2]}.rb" }
 watch(%r{^test/test_helper\.rb$}) { 'test' }

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

 # Rails 4
 watch(%r{^app/(.+)\.rb$}) { |m| "test/#{m[1]}_test.rb" }
 watch(%r{^app/controllers/application_controller\.rb$}) { 'test/controllers' }
 watch(%r{^app/controllers/(.+)_controller\.rb$}) { |m| "test/integration/#{m[1]}_test.rb" }
 watch(%r{^app/views/(.+)_mailer/.+}) { |m| "test/mailers/#{m[1]}_mailer_test.rb" }
 watch(%r{^lib/(.+)\.rb$}) { |m| "test/lib/#{m[1]}_test.rb" }
 watch(%r{^test/.+_test\.rb$})
 watch(%r{^test/test_helper\.rb$}) { 'test' }

 # Rails < 4
 # watch(%r{^app/controllers/(.*)\.rb$}) { |m| "test/functional/#{m[1]}_test.rb" }
 # watch(%r{^app/helpers/(.*)\.rb$}) { |m| "test/helpers/#{m[1]}_test.rb" }
 # watch(%r{^app/models/(.*)\.rb$}) { |m| "test/unit/#{m[1]}_test.rb" }
end