title: Rake - Don't know how to build task 'build'
body: <p>Apologies for a vague question. I haven't used Rake before and am trying to figure it out.</p>
  
  <p>I'm trying to run tests with rake but I get this stack trace when I do.</p>
  
  <pre><code>rake test:all --trace
  ** Invoke test:all (first_time)
  rake aborted!
  Don't know how to build task 'build'
  /Library/Ruby/Gems/2.3.0/gems/rake-10.4.2/lib/rake/task_manager.rb:62:in `[]'
  /Library/Ruby/Gems/2.3.0/gems/rake-10.4.2/lib/rake/task.rb:57:in `lookup_prerequisite'
  /Library/Ruby/Gems/2.3.0/gems/rake-10.4.2/lib/rake/task.rb:53:in `block in prerequisite_tasks'
  /Library/Ruby/Gems/2.3.0/gems/rake-10.4.2/lib/rake/task.rb:53:in `map'
  /Library/Ruby/Gems/2.3.0/gems/rake-10.4.2/lib/rake/task.rb:53:in `prerequisite_tasks'
  /Library/Ruby/Gems/2.3.0/gems/rake-10.4.2/lib/rake/task.rb:199:in `invoke_prerequisites'
  /Library/Ruby/Gems/2.3.0/gems/rake-10.4.2/lib/rake/task.rb:178:in `block in invoke_with_call_chain'
  /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/monitor.rb:214:in `mon_synchronize'
  /Library/Ruby/Gems/2.3.0/gems/rake-10.4.2/lib/rake/task.rb:172:in `invoke_with_call_chain'
  /Library/Ruby/Gems/2.3.0/gems/rake-10.4.2/lib/rake/task.rb:165:in `invoke'
  /Library/Ruby/Gems/2.3.0/gems/rake-10.4.2/lib/rake/application.rb:150:in `invoke_task'
  /Library/Ruby/Gems/2.3.0/gems/rake-10.4.2/lib/rake/application.rb:106:in `block (2 levels) in top_level'
  /Library/Ruby/Gems/2.3.0/gems/rake-10.4.2/lib/rake/application.rb:106:in `each'
  /Library/Ruby/Gems/2.3.0/gems/rake-10.4.2/lib/rake/application.rb:106:in `block in top_level'
  /Library/Ruby/Gems/2.3.0/gems/rake-10.4.2/lib/rake/application.rb:115:in `run_with_threads'
  /Library/Ruby/Gems/2.3.0/gems/rake-10.4.2/lib/rake/application.rb:100:in `top_level'
  /Library/Ruby/Gems/2.3.0/gems/rake-10.4.2/lib/rake/application.rb:78:in `block in run'
  /Library/Ruby/Gems/2.3.0/gems/rake-10.4.2/lib/rake/application.rb:176:in `standard_exception_handling'
  /Library/Ruby/Gems/2.3.0/gems/rake-10.4.2/lib/rake/application.rb:75:in `run'
  /Library/Ruby/Gems/2.3.0/gems/rake-10.4.2/bin/rake:33:in `&lt;top (required)&gt;'
  /usr/bin/rake:22:in `load'
  /usr/bin/rake:22:in `&lt;main&gt;'
  Tasks: TOP =&gt; test:all
  </code></pre>
  
  <p>What's the issue here? Is it likely something like a missing dependency?</p>