code: function Mocker(obj, methodName, mockFn) {
    this.obj = obj;
    this.methodName = methodName;
    this.originalFn = obj[methodName];
    this.history = [];
    
    //Assign new function
    mockFn = mockFn || this.originalFn;
    obj[methodName] = wrapFn(this, mockFn);
  }
docs: Mocker constructor
  
  @param {Object} obj            Object to create a mock of
  @param {String} methodName     Method name to mock
  @param {Function} mockFn       Mock function
  @return {Mocker}
  @api public