title: Sinon.js spy does not work correctly in mocha
body: <p>I have a mocha test case, where I want to spy on an existing functions. Unfortunately sinon.js does not count the calls:</p>
  
  <pre><code>    it("should work with spy", function() {
      var func = function() {
      };
  
      var spy = sinon.spy(func);
  
      func();
      func();
  
      console.log(spy.callCount);
  
      // fails
      assert(spy.CallCount == 2);
      /* works:
      var secondSpy = sinon.spy();
  
      secondSpy();
  
      console.log(secondSpy.callCount);
      */
  });
  </code></pre>
  
  <p>What could be probably be wrong?</p>