title: My doctest does not return correctly. What am I doing wrong
body: <p>I have the following files. If you look in app.ex the doctest says 2 + 2 is 3. 
  I am intentionally trying to make it fail.</p>
  
  <p><strong>app.ex</strong></p>
  
  <pre><code>defmodule App do
       @doc """
        Adds two numbers
  
        ## Examples
  
          iex&gt; App.add(2, 2)
          3
  
        """
      def add(a,b) do
        a + b
      end
  
  
  end
  </code></pre>
  
  <p><strong>app_test.exs</strong></p>
  
  <pre><code>defmodule AppTest do
    use ExUnit.Case
  
    doctest App
  end
  </code></pre>
  
  <p>In the console I type: <code>mix test</code> and the result is:</p>
  
  <pre><code>Finished in 0.01 seconds
  0 failures
  
  Randomized with seed 547000
  </code></pre>