title: Most idiomatic way in NUnit to assert equal length on collections
body: <p>What's the most idiomatic way with NUnit 2.6 to assert that two collections are of equal length regardless of their elements' values?</p>
  
  <p>I can see several ways of expressing that assertion. Which one is preferred, or are there disadvantages/advantages with using one or the other?</p>
  
  <pre><code>Assert.That(coll1, Has.Count.EqualTo(coll2.Count));
  Assert.That(coll1.Count, Is.EqualTo(coll2.Count));
  Assert.AreEqual(coll1.Count, coll2.Count);
  </code></pre>
  
  <p>I can see that the first option provides a nice output in case the assertion failed (Expected count of ... but actually got ...), whereas the other two options only output "Expected ..., actual ..." unless I provide a custom message through an additional parameter.</p>