title: In Scala Specs, what is the "must" function?
body: <p>I'm working with some Specs tests and I'm trying to understand what the "must" function is, and what it does.</p>
  
  <p>I am unable to find its declaration or implementation anywhere in the specs source, and I'm trying to understand what it does.</p>
  
  <p>Here are some example usages of it:</p>
  
  <pre><code>"hello world".size must be equalTo(11)
  "hello world" must be matching("h.* w.*")
  stack.push(11) must throwAn[Error]
  </code></pre>
  
  <p>It looks to me like "must" takes a function as an argument, but I'd like to know the actual signature of "must", and what it does with its argument.</p>
  
  <p>Can anyone point me in the right direction?</p>
  
  <p>Thanks!</p>