title: Using RSpec, are constants within describes a big no-no?
body: <p>I just spent ages trying to figure out why my specs were passing in isolation, but when running the controller and lib tests together, some specs were mysteriously failing.  The culprit was this:</p>
  
  <p>In one spec:</p>
  
  <pre><code>describe SomeThing do
    CONSTANT_VALUE = "a value"
  
    # ... examples etc ...
  end
  </code></pre>
  
  <p>And in another:</p>
  
  <pre><code>describe AnotherThing do
    CONSTANT_VALUE = "a different value"
  
    # ... the rest is history
  end
  </code></pre>
  
  <p>The values I'd assigned to these constants was leaking between my specs and causing unexpected behaviour.  Am I supposed to use a <code>let</code> block for defining constants etc?  Or something else?</p>