title: Why do we need to install minitest gem sometimes?
body: <p>I am using Ruby 2.0.</p>
  <p>Sometimes I encounter cases where I can't just simply <code>require 'minitest'</code>. It gives me</p>
  <pre><code>irb&gt; require 'minitest'
  LoadError: cannot load such file -- minitest
  from rubygems/core_ext/kernel_require.rb:55:in `require'
  </code></pre>
  <p>I need to install minitest gem first. However I thought minitest is bundled in the Ruby standard library.</p>
  <p>When do we need to explicitly install minitest gem via <code>gem install</code> or Gemfile?</p>
  <p>If installing explicitly is required, should Gemfile <code>bundle install</code> preferred over <code>gem install</code>?</p>
  <h3>update</h3>
  <p>I myself use rbenv. I install my Ruby through rbenv as well.<br />
  My ruby version is ruby 2.0.0p353 (2013-11-22 revision 43784) [x86_64-darwin13.0.2]</p>