title: How to match a function with chai.should
body: <p>Let say that a function should return the following</p>
  
  <pre><code>{ key: 'bar',
    cb: () =&gt; {},
    ...
  }
  </code></pre>
  
  <p>The question is now how I can validate this in a unit test. If I do for example</p>
  
  <pre><code>getFunc().should.eql({key: 'bar', cb: () =&gt; {}, ...});
  </code></pre>
  
  <p>it always fails because the <code>cb</code> value is a different function
  Does <code>Chai.should</code> have an equivalent of <code>jasmine.any(Function)</code> ? or how is this done with chai.should ? </p>