title: Ruby Koan 151 raising exceptions
body: <p>I'm going through the ruby koans, I'm on 151 and I just hit a brick wall.</p>
  
  <p>Here is the koan:</p>
  
  <pre><code># You need to write the triangle method in the file 'triangle.rb'
  require 'triangle.rb'
  
  class AboutTriangleProject2 &lt; EdgeCase::Koan
    # The first assignment did not talk about how to handle errors.
    # Let's handle that part now.
    def test_illegal_triangles_throw_exceptions
      assert_raise(TriangleError) do triangle(0, 0, 0) end
      assert_raise(TriangleError) do triangle(3, 4, -5) end
      assert_raise(TriangleError) do triangle(1, 1, 3) end
      assert_raise(TriangleError) do triangle(2, 4, 2) end
   end
  end
  </code></pre>
  
  <p>Then in triangle.rb we have:</p>
  
  <pre><code>def triangle(a, b, c)
    # WRITE THIS CODE
    if a==b &amp;&amp; a==c
      return :equilateral
    end
    if (a==b &amp;&amp; a!=c) || (a==c &amp;&amp; a!=b) || (b==c &amp;&amp; b!=a)
      return :isosceles
    end
    if a!=b &amp;&amp; a!=c &amp;&amp; b!=c
      return :scalene
    end
    if a==0 &amp;&amp; b==0 &amp;&amp; c==0
      raise new.TriangleError
    end
  
  
  
  end
  
  # Error class used in part 2.  No need to change this code.
  class TriangleError &lt; StandardError
  
  end
  </code></pre>
  
  <p>I am beyond confused - any help at all would be much appreciated!</p>
  
  <p>EDIT: To complete this koan, I need to put something in the TriangleError class - but I have no idea what</p>
  
  <p>UPDATE: Here is what the koan karma thing is saying:</p>
  
  <pre><code>&lt;TriangleError&gt; exception expected but none was thrown.
  </code></pre>