title: double.NaN Equality in MS Test
body: <p>Why am I getting this result?</p>
  
  <pre><code>[TestMethod]
  public void nan_test()
  {
      Assert.AreEqual(1, double.NaN, 1E-1); &lt;-- Passes
      Assert.AreEqual(1, double.NaN);       &lt;-- Fails
  }
  </code></pre>
  
  <p>What difference does the delta have in asserting NaN equals a number? Surely it should always return false. I am aware of IsNaN, but that's not useful here (see below).</p>
  
  <p>Background: I have a function returning NaN (erroneously) , it was meant to be a real number but the test still passed. I'm using the delta because it's double precision equality, the original test used 1E-9.</p>