title: cannot load such file -- test_helper if test case run using 'ruby' instead of 'rake test'
body: <p>If I run test case:</p>
  
  <pre><code>ruby test/models/chat_bot/option_test.rb
  </code></pre>
  
  <p>I get error:</p>
  
  <pre><code>/home/anuja/.rvm/rubies/ruby-2.3.1/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require': cannot load such file -- test_helper (LoadError)
  </code></pre>
  
  <p>and it works if I run test as follow:</p>
  
  <pre><code>rake test test/models/chat_bot/option_test.rb
  </code></pre>