我在Ruby 2.1.5p273上运行Ruby on Rails 2.3.18应用程序，当我运行单元测试套件时，我在终端中获得此输出
dminca@dev:$ bundle exec rake test:units
* ruby 2.1.5p273 (2014-11-13 revision 48405) [x86_64-linux]
* /home/dminca/.rvm/gems/ruby-2.1.5/bin/rake
* pid: 32205
* Using RAILS_ENV for ENV_CONFIG: development
* configuring for environment: development
* loaded .env .env.development
* configuring LOGGING: file
LOG_FILE: development.log
LOG_PATH: log
LOG_FILE_PATH: /home/dminca/Projects/mld/application/log/development.log
LOG_LEVEL: debug
* configuring TRACKER: Utility::Tracker::Stdout
/home/dminca/.rvm/rubies/ruby-2.1.5/bin/ruby -I"lib:test" -I"/home/dminca/.rvm/gems/ruby-2.1.5/gems/rake-0.9.6/lib" "/home/dminca/.rvm/gems/ruby-2.1.5/gems/rake-0.9.6/lib/rake/rake_test_loader.rb" "test/unit/**/*_test.rb"
/home/dminca/Projects/mld/application/test/unit/helpers/cms/app_texts_helper_test.rb:1:in `require': cannot load such file -- test_helper (LoadError)
from /home/dminca/Projects/mld/application/test/unit/helpers/cms/app_texts_helper_test.rb:1:in `<top (required)>'
from /home/dminca/.rvm/gems/ruby-2.1.5/gems/rake-0.9.6/lib/rake/rake_test_loader.rb:10:in `require'
from /home/dminca/.rvm/gems/ruby-2.1.5/gems/rake-0.9.6/lib/rake/rake_test_loader.rb:10:in `block (2 levels) in <main>'
from /home/dminca/.rvm/gems/ruby-2.1.5/gems/rake-0.9.6/lib/rake/rake_test_loader.rb:9:in `each'
from /home/dminca/.rvm/gems/ruby-2.1.5/gems/rake-0.9.6/lib/rake/rake_test_loader.rb:9:in `block in <main>'
from /home/dminca/.rvm/gems/ruby-2.1.5/gems/rake-0.9.6/lib/rake/rake_test_loader.rb:4:in `select'
from /home/dminca/.rvm/gems/ruby-2.1.5/gems/rake-0.9.6/lib/rake/rake_test_loader.rb:4:in `<main>'
rake aborted!
Command failed with status (1): [ruby -I"lib:test" -I"/home/dminca/.rvm/gems/ruby-2.1.5/gems/rake-0.9.6/lib" "/home/dminca/.rvm/gems/ruby-2.1.5/gems/rake-0.9.6/lib/rake/rake_test_loader.rb" "test/unit/**/*_test.rb" ]
/home/dminca/.rvm/gems/ruby-2.1.5/bin/ruby_executable_hooks:15:in `eval'
/home/dminca/.rvm/gems/ruby-2.1.5/bin/ruby_executable_hooks:15:in `<main>'
Tasks: TOP => test:units
(See full trace by running task with --trace)
如何使测试有效？